Iran has reduced missile fire at Israel, which may be part strategy, part necessity.

Israel’s prime minister, Benjamin Netanyahu, wants the United States to drop its largest bunker-busting bombs on Iran’s Fordo nuclear site, which lies deep underground. Israel has neither bombs that big nor warplanes big enough to carry them.

In a post on Truth Social, Mr. Trump wrote, “we know exactly where” Ayatollah Ali Khamenei, Iran’s supreme leader, “is hiding,” but added, “we are not going to take him out (kill!), at least for now.” Boasting of Israel’s air superiority, which he suggested was based on American technology, he wrote, “We now have complete and total control of the skies over Iran,” associating himself with Israel’s war effort.

Earlier in the day, Mr. Trump said he was looking for something “better than a cease-fire” between Israel and Iran — “a real end, not a cease-fire.” Speaking to reporters on Air Force One, Mr. Trump, who departed Monday, a day early, from a meeting of leaders of the Group of 7 nations in Alberta, Canada, said he wanted Iran to give up while insisting that Tehran abandon any effort to develop nuclear weapons. “I’m not too much in the mood to negotiate,” he added.

Here’s what else to know:

• Israeli strikes: Attacks were reported Tuesday in Tehran and western Iran. The Israeli military’s chief spokesman, Brig. Gen. Effie Defrin, said in a televised briefing that Iran still retained “significant capabilities that could cause serious damage.”

• Iranians flee: Evacuations from Tehran have intensified in the hours since the Israeli military issued an evacuation order for a large part of northeastern Tehran, saying it planned to target “military infrastructure” in the area.

• Iranian general: Israel said it had killed Maj. Gen. Ali Shadmani in an airstrike, describing him as Iran’s top military commander, just four days after he was appointed to replace another general killed in a separate airstrike. Iran has not confirmed the death of General Shadmani, but its military hierarchy has been decimated by the Israeli bombing.

• Natanz nuclear site: Israeli airstrikes achieved “direct impacts” on the underground area of the Natanz nuclear site, where Iran enriches uranium, the United Nations’ chief nuclear monitor said on Tuesday, based on new satellite images. That indicates more serious damage than previous assessments of the attack on Friday.

• Internet disrupted: Internet services across Iran are suffering severe disruptions, according to experts and Iranians, who say the government is likely restricting access to limit the spread of information about strikes and for fear of Israeli cyberattacks.

In the first days of the war, Iran fired as many as almost 100 missiles in a single night, in salvos of dozens. But overnight into Tuesday, fewer than 30 projectiles breached Israeli airspace. An early morning salvo included just a few missiles — far fewer than in previous waves — according to Lt. Col. Nadav Shoshani, an Israeli military spokesperson.

Since the fighting began on Friday, there have been more than 35 direct hits on Israeli military facilities, a research university, an oil refinery and residential areas. The Iranian missiles have killed at least 24 people, injured hundreds and left over 2,000 people homeless, according to the Israeli Prime Minister Office. Israel successfully intercepts most incoming missiles with its advanced air defense systems, and is trying to strip Iran of its ability to launch missiles by targeting its launchers and stockpiles. Brig. Gen. Effie Defrin, the military’s chief spokesperson, said that the Israeli air force had destroyed more than 120 surface-to-surface launchers, which he said was about one-third of Iran’s arsenal.

The slowdown in Iran’s missile fire may indicate that Israeli strikes have significantly damaged Tehran’s ability to launch projectiles. But it could also suggest that Iranian leaders are preparing for a conflict that may stretch on for weeks or even months.

Israel initially estimated that Iran had around 2,000 ballistic missiles before the war began. After firing roughly 400 and sustaining hits to some of its stockpiles, Israeli experts and officials now believe Iran still has over 1,000 ballistic missiles.

“Iran cannot sustain a pace of hundreds of missiles per night for very long — they’ll run out of stock,” said Raz Zimmt, director of the Iran and Shiite Axis research program at the Institute for National Security Studies, an Israeli think tank. “But if they spread it out, they can drag Israel into a war of attrition.”

Iran at first attempted to overwhelm Israel’s defense systems by launching large volleys of missiles simultaneously. But as its ability to fire massive barrages diminishes, Israel’s interception capabilities become more effective. This is critical, because ballistic missiles are Tehran’s primary offensive tool against Israel and crucial to its ability to retaliate.

Despite the Israeli defenses, some missiles appear to have struck on Tuesday. Videos verified by The New York Times show several explosions close to key Israeli military sites near the town of Ramat Hasharon, north of Tel Aviv.

While Iran’s armed forces are among the largest in the Middle East, with at least 580,000 active-duty personnel, their ability to reach Israel — over 600 miles away — is limited by an outdated air force. Iranian-backed militias that sometimes act as proxies in attacking Israel, such as Hezbollah in Lebanon and Hamas in Gaza, have been significantly weakened over the past two years and cannot provide meaningful support.

Even so, Israel remains concerned that Iran may still find new ways to fight back.

For days, Iranians have described worsening problems as they tried to contact loved ones, get reliable news, access their bank accounts online or simply connect to the internet. The restrictions may also be affecting people’s ability to see warnings related to the war, like one the Israeli military made on Monday, when it told people in part of Tehran to evacuate because of an imminent strike.

Netblocks, an internet monitoring group, reported on Tuesday that an “analysis of telemetry shows a significant reduction in internet traffic” in Iran, showing a graphic with a steep decline.

“It seems like we’re headed toward a full disconnection,” said Amir Rashidi, a cybersecurity expert based in the United States.

Several Iranians around the country said in interviews that mobile data networks were down in parts of Iran, making it impossible for many people to access foreign mobile apps and websites on their phones — only domestic sites and apps remained active. They reported that the virtual private networks, or V.P.N.s, that Iranians use to access the internet free of restrictions were being blocked intermittently.

“They disconnected WhatsApp; then they connected it; then they disconnected it again,” said Arta, a 28-year-old from Tehran, via text. “When you’re on cellular, V.P.N. connects in some places and not in others. They’ve closed most of the ports.”

The government has urged people to use the N.I.N., which allows people to message only using government platforms — software that many people don’t trust or believe to be secure.

For decades, the Iranian government has restricted access to certain websites and social media applications, such as Facebook or Instagram, and many Iranians have relied on a collection of V.P.N.s to bypass the government’s filters.

But since Israel began attacking Iran last week, many people have said that their V.P.N. services were failing, forcing them to have to search for working ones or to try “hopping” from one network to another.

The disruptions so far do not appear to be uniform, though many believe that the government is trying to prevent people from sharing information about where Israel has struck, including sharing photos or videos.

There also appears to be intense security around such strikes, making it difficult to assess the damage and civilian toll. In some videos that have been shared, people can be heard asking others “not to film” and “not to block the way” for emergency services.

In the absence of reliable information, some Iranians have described a sense of panic, with people sharing tips about what GPS and messaging apps to use if the government restricts the internet entirely, save for the N.I.N. “Google Play isn’t showing routes correctly,” Mr. Rashidi said, “so some people who were trying to evacuate are now lost.”

The Iranian authorities have warned people against using apps like WhatsApp, saying that the country is under cyberattack from Israel.

Leily Nikounazar contributed reporting.

Many of the Iranians interviewed, all of whom asked to be identified only by their first names because of the sensitivity of the situation, are struggling to absorb their new, ever-changing reality.

Crowds of Iranians have fled Tehran since Israel launched an attack on Friday. Evacuations have intensified in the hours since the Israeli military issued an evacuation order for a large part of northeastern Tehran, saying it planned to target “military infrastructure” in the area.

Some gas stations have reportedly closed because they ran out of fuel, and social media footage verified by The New York Times showed traffic clogging roads leading out of Tehran.

Israel’s attacks have killed more than 224 people and injured more than 1,800 people in Iran, according to the country’s health ministry. Iranian strikes have killed more than 24 people and injured more than 600 in Israel, according to the Israeli government.

“Before this conflict erupted, we used to joke in group chats and online that the next disaster would be something absurd like a volcanic eruption, an alien invasion or a zombie attack,” Kimia said. “What we didn’t think about was another war.”

She has been glued to the news, and she said her life has become a maelstrom of stress, worry and uncertainty.

“It felt like all of Tehran was evacuating,” said Fahimeh, the jewelry designer from Tehran. Fuel lines were so long that she skipped refueling, and while she did not notice a grocery shortage, she was only allowed to buy two cans of tuna.

“Drivers were aggressively overtaking each other, showing little patience or empathy,” Fahimeh said. “People seemed frustrated and anxious. My foot was constantly on the clutch and brake.”

Leili, a teacher who lives in the province of Mazandaran, said many Iranians were starting to seek refuge in her area.

Grocery shortages there were becoming increasingly noticeable, she said, and meat and chicken were becoming hard to find.

“Cooking oil is now scarce in stores, and if this continues, the situation could grow more concerning,” she said. While she hasn’t stockpiled supplies, Leili said, “many others have begun hoarding, likely driven by memories of shortages during the Iran-Iraq war and fears of future scarcity.”

Many Iranians are experiencing a mix of emotions, a concern for their homeland and its future, alongside satisfaction at the regime’s humiliation, Leili added. There are questions about what the war will mean for the nation’s political future, too.

If the regime was overthrown, Masoud wondered, would the United States intervene to set up a new Western-style secular democracy, as he and others he knew hoped? Or would Israel and the United States “destroy the regime and then abandon Iran to its fate,” as Masoud said most people he spoke to feared?

“People are terrified of the uncertain fate that awaits them. Like walking in the dark, when you can’t see ahead, you are most afraid,” Masoud said.

Both Iran and Israel have ignored possible routes toward de-escalation. And on Tuesday morning, President Trump said he wanted something “better than a cease-fire,” adding he wanted a “complete give-up” by Iran.

“The small routines and plans I had for my life are shattered,” Kimia said. “I can no longer envision a future beyond ensuring the safety of my loved ones and bracing for the worst if something happens to them.”

“From an official diplomatic posture perspective, the Israelis will not confirm or deny” their nuclear arsenal, said Alexander K. Bollfrass, a nuclear security expert at the International Institute for Strategic Studies in London.

Instead, Israel has said it will not be the first country to “introduce” nuclear weapons to the Middle East. That deliberately vague wording amounts to what Mr. Bollfrass called an “obfuscation over what is clearly an established nuclear weapons program.”

How big is Israel’s nuclear arsenal?

Israel is widely believed to have at least 90 warheads and enough fissile material to produce up to hundreds more, according to the Center for Arms Control and Nonproliferation and the Nuclear Threat Initiative.

The International Atomic Energy Agency, the nuclear watchdog for the United Nations, has assessed that 30 countries are capable of developing nuclear weapons but only nine are known to possess them. Israel has the second-smallest arsenal among the nine, ahead only of North Korea, according to a Nobel Prize-winning advocacy group, the International Campaign to Abolish Nuclear Weapons. Israel could fire warheads from fighter jets, submarines or ballistic missile ground launchers, experts said.

Israel is one of five countries — joining India, Pakistan, North Korea and South Sudan — that is not a signatory to the U.N. Nuclear Nonproliferation Treaty. The agreement, which came into force in 1970, generally commits governments to promoting peaceful uses of nuclear energy and preventing the spread of nuclear weapons.

(Iran is a signatory to the treaty, although Israel and world powers have accused Tehran of violating it by unnecessarily enriching uranium at high enough levels to build a nuclear weapon.)

Israel would have to give up its nuclear weapons to sign the treaty, which recognizes only five countries as official nuclear states: Britain, China, France, Russia and the United States — the permanent members of the U.N. Security Council. All had detonated a nuclear weapon by 1967, the cutoff date in the treaty to qualify for the designation.

How long has Israel had nuclear weapons?

Israeli leaders were intent on building a nuclear arsenal to safeguard the country’s survival soon after it was founded in 1948 in the wake of the Holocaust, historical records indicate.

The Israel Atomic Energy Commission was established in 1952, and its first chairman, Ernst David Bergmann, said that a nuclear bomb would ensure “that we shall never again be led as lambs to the slaughter,” according to the Jewish Virtual Library.

Israel began building a nuclear weapons development site in 1958, near the southern Israeli town of Dimona, researchers believe. A recently declassified U.S. intelligence report from December 1960, by the Joint Atomic Energy Intelligence Committee, stated that the Dimona project included a reprocessing plant for plutonium production. The report concluded that the project was related to nuclear weapons.

Around 1967, Israel secretly developed the ability to build nuclear explosives, according to the Arms Control Association. By 1973, the United States “was convinced Israel had nuclear weapons,” the Federation of American Scientists later wrote.

Israel is not among the three dozen countries — all in Europe or Asia — considered to be protected by the United States’ so-called nuclear umbrella. That protection not only serves as an American deterrent against adversaries but also aims to encourage the countries not to develop their own nuclear weapons.

Experts said that the fact that Israel was not part of the American nuclear umbrella was another unspoken acknowledgment that Israel had its own atomic weapons and did not need protection or deterrence.

“Ultimately, there is a sense of responsibility that Israel’s security rests with Israel, and they will do what is necessary to provide for that,” Mr. Bollfrass said.

Has Israel used its nuclear weapons in war?

No.

The Jewish Virtual Library, which is considered among the world’s most comprehensive Jewish encyclopedias, has cited reports that Israel prepared its nuclear bombs during the Arab-Israeli wars of 1967 and 1973, but the weapons were not used.

There have been a few reports over the past 50 years that Israel has tested its nuclear weapons at underground sites, including in the Negev desert in southern Israel.

The most prominent episode — and one that remains under debate — was in September 1979, when an American satellite designed to detect nuclear explosions reported a double flash near where the South Atlantic and Indian oceans meet. Some scientists believed that the double flash was likely to have been the result of a nuclear test, by Israel or South Africa, or possibly by both.

Israel denied involvement in what is known as the Vela incident, for the satellite’s name. Former President Jimmy Carter’s White House diaries, published in 2010, cited “growing belief” at the time that Israel had tested a nuclear explosion near the southern tip of South Africa. But that was never proven, and “relevant documents for the Vela incident are still classified,” the scientists Avner Cohen and William Burr wrote in 2020, citing the diaries.

Where does Israel build its nuclear weapons?

It’s widely believed that Israel’s nuclear weapons program is housed in Dimona.

Experts said it appeared that inspectors from the International Atomic Energy Agency had never been to the site, and that there was no agreement with Israel that would allow the U.N. watchdog agency to monitor it. American scientists visited Dimona in the 1960s and concluded that the nuclear program there was peaceful, based on increasingly limited inspections, historical records show. But there is no public evidence that American inspectors have been back since.

Satellite photos show new construction at Dimona over the past five years. At a minimum, experts said, the facility is undergoing repairs and much-needed modernization.

There is also a growing belief among some experts that Israel is building a new reactor in Dimona to increase its nuclear capability. A report released this week by the Stockholm International Peace Research Institute said Israel appeared to be upgrading a reactor site there to produce plutonium, which can be used both for nuclear weapons and some peaceful purposes, like in space.

Because of its secrecy, Dimona has long been a symbol of fascination and, to some, anger over Israel’s nuclear weapons program.

In a rare public event at the site in 2018, Prime Minister Benjamin Netanyahu of Israel used it as a backdrop to warn enemies that “those who threaten to wipe us out put themselves in a similar danger — and in any event will not achieve their goal.”

Several Iranians around the country said in interviews that mobile data networks were down in parts of Iran, making it impossible for many people to access foreign mobile apps and websites on their phones — only domestic sites and apps remained active. They reported that the VPNs that Iranians use to access the internet free of restrictions were being blocked intermittently.

Although analysts said the group remained a threat, it was unclear how much firepower Hezbollah could bring to bear after losing much of its arsenal and many of its senior commanders during its 14-month war with Israel.

Once a formidable militia, Hezbollah was left battered by the conflict and has struggled to recover under a fragile cease-fire signed in November. As a result, the group has little incentive to risk provoking a new Israeli offensive, according to analysts.

Hezbollah's absence from the fighting in recent days underscored the new reality for a group long positioned by Tehran as its first line of defense against Israel and reflected the broader weakening of Iran’s network of regional allies and proxies.

After Israel began airstrikes inside Iran on Friday, Lebanon’s government relayed messages to Hezbollah via the Lebanese military, urging the group not to intervene, according to one of the Lebanese officials. Lebanon’s new government has pledged to disarm all armed groups inside the country, including Hezbollah, but has yet to set a timeline on the process.

Those messages were echoed on Monday by Lebanon’s president and prime minister who stressed — without naming Hezbollah directly — that the country must stay out of the conflict. The crisis-hit nation is still reeling from Lebanon’s deadliest war in decades, with swaths of the country in ruins and no indication who will foot the multibillion-dollar reconstruction bill.

During a cabinet session on Monday, President Joseph Aoun insisted on “making every possible effort to keep Lebanon away from conflicts that do not concern it,” according to a statement from his office.

Western officials have similarly cautioned Hezbollah in recent days to stay out of the fighting, according to a senior Western diplomat who communicates with the militant group. Hezbollah so far appears to be wary of making a misstep and understands that any attack against Israel from Lebanon would not serve its interests, said the official, who requested anonymity to discuss the sensitive issue.

Hezbollah’s media office did not immediately respond to a request for comment. The group said in a statement on Friday that Israel’s attack on Iran was a dangerous escalation that threatened to “ignite the entire region,” but it notably stopped short of any pledge to respond militarily.

However, Lebanon is also home to an array of other armed groups, among them Palestinian factions including Hamas, whose primary power base is the Gaza Strip, where Israel is in the midst of another war.

Hamas was accused in March of firing rockets into Israel from Lebanon, one of many actions on both sides of the conflict in defiance of the cease-fire. Hours later, the Israeli military carried out airstrikes in Beirut’s southern suburbs for the first time in months, leading the Lebanese government to issue stern warnings to Hamas and arrest several Palestinian operatives.

Fearing a repeat of such rocket fire, the Lebanese military has moved to bolster its presence and enforce security measures in southern Lebanon in recent days, according to two senior Lebanese security officials who requested anonymity to discuss sensitive military matters.

The reinforced measures include increased army patrols and more vehicle searches at checkpoints, which are intended to prevent militants from firing into Israel from Lebanon and triggering an escalation, one official said.

Lebanon’s prime minister, Nawaf Salam, said on Monday that Lebanon must be spared “any involvement, in any form, in the ongoing conflict,” according to a government statement.

Hwaida Saad contributed reporting.

While Mr. Trump suggested that the United States had control of Iran’s skies, the only visible combatant has been Israel, which has been using American-made fighter jets. Israeli officials have said that they have been able to destroy much of Iran’s air defenses.

In one of his messages Tuesday, Mr. Trump threatened Iran’s supreme leader, Ayatollah Ali Khamenei, saying “we know exactly where” he is. But he added that “we are not going to take him out (kill!), at least for now.” Killing foreign leaders is against the law in the United States.

He added, “Our patience is growing thin.”

In his own social media post, Vice President JD Vance also hinted that the United States could step up its engagement. Mr. Vance said that Iran has no need for nuclear fuel enriched above the level needed for commercial power. Mr. Trump, he wrote, “has shown remarkable restraint,” but “may decide he needs to take further action to end Iranian enrichment.”

“That decision ultimately belongs to to the president,” Mr. Vance wrote.

The vice president acknowledged the sentiments of some in the Republican Party who have called for staying out of conflicts in the Middle East, writing “of course, people are right to be worried about foreign entanglement after the last 25 years of idiotic foreign policy,” a period of time that encompasses Mr. Trump’s first term and the Bush, Obama and Biden administrations. But, he added, “I believe the president has earned some trust on this issue.”

It remains to be seen whether Mr. Trump will ultimately decide that the United States should join Israel’s efforts, with American offensive capability. On Monday, Defense Secretary Pete Hegseth said only that American forces were maintaining a “defensive posture.”

On his flight back to Washington from Canada, Mr. Trump told reporters on Air Force One that he was not in the mood to continue negotiations with Iran, which were scheduled for last Sunday before Israel began mounting its attacks.

Mr. Trump said that he was seeking a result that was “better than a cease-fire” between Israel and Iran. Asked what would qualify, he said “an end, a real end, not a cease-fire, a real end.”

But as Israel pounds Iran with airstrikes that it says are aimed at the country’s nuclear and missile programs, analysts say the assault increasingly threatens the survival of Iran’s government and may in effect be turning into a regime change operation.

That could leave Mr. Trump trying to avoid entanglement in the sort of conflict he has spent years portraying as the definition of insanity.

Israeli officials say their attacks are an urgent response to Iran’s advances in its nuclear program. But there are growing signs that their aims are expanding.

During an interview on Fox News on Monday, Prime Minister Benjamin Netanyahu of Israel was asked whether regime change was an explicit goal.

“It could certainly be the result, because Iran is very weak,” he said. He added that “the decision to act, to rise up, at this time, is the decision of the Iranian people.”

But Mr. Netanyahu has also appealed to Iran’s population — which has risen in protest many times in recent years, only to be brutally repressed — to do just that. “The time has come for you to unite around your flag and your historic legacy by standing up for your freedom from an evil and oppressive regime,” he said last week.

In a Monday interview with ABC News, Mr. Netanyahu also said that Israel might choose to “end the conflict” by killing Iran’s supreme leader, Ayatollah Ali Khamenei.

“This is the name of the game,” said Vali Nasr, a professor at the Johns Hopkins School of Advanced International Studies.

“It’s not how successful Israel is in taking out Fordo,” the Iranian nuclear facility buried deep in a mountain. “It is now measured by how successful they can be in taking out the Iranian state.”

Mr. Nasr noted that Israel has been striking targets with no direct connection to Iran’s nuclear program, including a Monday attack on the headquarters of Iran’s state broadcasting network. “They are trying to take away the coherence of the state — not only to conduct the war, but to function,” he said.

Mr. Trump has so far limited America’s known role to the defense of Israel. But in a post on Truth Social on Tuesday, he suggested a willingness to eliminate Mr. Khamenei, saying “we know exactly where” he is hiding. “We are not going to take him out,” he wrote, adding: “At least not for now.”

And the president associated himself with Israel’s war effort, writing in a separate post: “We now have complete and total control of the skies over Iran,” with the support of American military hardware. (Despite Mr. Trump’s use of “we,” the United States is not flying missions over Iran, U.S. officials say.)

A full collapse of the Iranian state, meanwhile, would create new risks — including the need to secure Iran’s nuclear material — that would greatly increase the prospects of American involvement in the conflict.

Israel’s primary goal may be the destruction of Iran’s nuclear program, said Michael Makovsky, president and chief executive of the Jewish Institute for National Security of America, which has backed military action against Iran.

Mr. Makovsky added, however, based on his conversations with senior political and military officials there, that Israel has always known that such a campaign could also have broader political consequences.

“They’ve hoped that, because the regime was so weak, military action could lead to the people bringing down the regime,” he said.

Iran’s leadership may share that assessment. In April, The New York Times reported that Mr. Khamenei agreed to nuclear talks with President Trump earlier this year only after top Iranian officials warned him that failure to negotiate could lead to attacks by Israel or the United States. That, they said, could threaten the survival of their government.

Even some supporters of using force to seek a change in Iran’s government are careful to avoid the catchphrase that was used often during the Iraq War and subsequent Western interventions in the Middle East. They include the 2011 NATO air campaign in Libya that overthrew the dictator Muammar Gaddafi but triggered years of chaos and civil war.

Mr. Trump himself has tried to engineer the fall of at least one foreign government, the leftist dictatorship of Venezuela’s Nicolas Maduro, which he choked with economic sanctions in his first term. But he never described his policy as regime change.

“I use the term ‘regime collapse,’ versus ‘change,’” Mr. Makovsky said, “because the term ‘regime change’ is toxic in Washington. Everyone thinks about 2003.”

In March of that year, President George W. Bush invaded Iraq and deposed its strongman, Saddam Hussein. The ensuing effort to install a friendly democratic government in Baghdad cost thousands of American lives and hundreds of billions of dollars, and to many, discredited U.S. interventionism.

The key distinction, Mr. Makovsky said, is that a regime collapse strategy does not presume to remake Iran’s government. “My view is that we shouldn’t do that. But our objective should be to pressure the regime every way possible so that the Iranian people bring it down.”

For now, Mr. Trump has kept some distance from Israel’s war. But his supporters are divided on his approach, with some accusing Mr. Trump of betraying his principles.

On Monday, two of Mr. Trump’s most prominent supporters, the former Fox News host Tucker Carlson and the former Trump White House aide Steve Bannon vented their frustration on a radio show hosted by Mr. Bannon.

“The point of this is regime change,” Mr. Carlson insisted, arguing that Mr. Trump was being led by Israel into what could become a “world war.” “I don’t want the United States involved in another Middle East war,” he added.

Mr. Bannon agreed, citing Mr. Netanyahu’s comments on Fox and saying, “This is a total regime change.”

“This thing has not been thought through,” he added. “It does not have the support of the American people.”

Analysts said it would be especially difficult for Mr. Trump to avoid being drawn into the aftermath of a government collapse. “The U.S. just can’t not be involved,” said Mr. Nasr, noting that, among other things, it would be essential to secure Iran’s stockpile of uranium amid any political chaos.

Some analysts fear that Iran could descend into chaos and even civil war, radiating instability throughout the Middle East. Although one U.S. official said that Mr. Khamenei had put in place a succession plan, and that in the event of his killing or overthrow Iran’s religious-military establishment would be likely to retain control — possibly with an even more extreme figure.

Even so, few in Washington would mourn the fall of a theocracy that sponsors terrorism and has spent 40 years calling for the destruction of America and Israel. And some prominent Republicans are calling for that outcome.

“I think it is very much in the interest of America to see regime change,” Senator Ted Cruz of Texas said on Fox News on Sunday. “I don’t think there’s any redeeming the ayatollah.”

Another Republican senator, Lindsey Graham of South Carolina, told CBS News on Sunday he would “love for the regime to fall,” but added that “is not the purpose of this attack — yet.”

Ben Rhodes, a former deputy national security adviser under President Obama who was deeply involved in Iran policy, said that even some Democrats are wondering whether to root for Iran’s government to collapse.

Mr. Rhodes fears that initial success of Israel’s military campaign has created the illusion of a simple solution, something that reminds him of the early stages of another Middle East conflict more than 20 years ago.

“It looked great when the statue of Saddam Hussein fell” in the spring of 2003, Mr. Rhodes said.

A pro-Israel hacking group called Predatory Sparrow, or in Farsi, Gonjeshke Darand, claimed responsibility, saying that the bank had financed terrorism using money from the accounts of the Iranian people.

But this time, the American intelligence assessment was that Mr. Netanyahu was preparing not just a limited strike on the nuclear facilities, but a far more expansive attack that could imperil the Iranian regime itself — and that he was prepared to go it alone.

The intelligence left President Trump facing difficult choices. He had become invested in a diplomatic push to persuade Iran to give up its nuclear ambitions, and had already swatted down one attempt by Mr. Netanyahu, in April, to convince him that the time was right for a military assault on Iran. During a strained phone call in late May, Mr. Trump again warned the Israeli leader against a unilateral attack that would short-circuit the diplomacy.

But over the last several weeks, it became increasingly apparent to Trump administration officials that they might not be able to stop Mr. Netanyahu this time, according to interviews with key players in the administration’s deliberations over how to respond and others familiar with their thinking. At the same time, Mr. Trump was getting impatient with Iran over the slow pace of negotiations and beginning to conclude that the talks might go nowhere.

Contrary to Israeli claims, senior administration officials were unaware of any new intelligence showing that the Iranians were rushing to build a nuclear bomb — a move that would justify a pre-emptive strike. But seeing they would most likely not be able to deter Mr. Netanyahu and were no longer driving events, Mr. Trump’s advisers weighed alternatives.

At one end of the spectrum was sitting back and doing nothing and then deciding on next steps once it became clear how much Iran had been weakened by the attack. At the other end was joining Israel in the military assault, possibly to the point of forcing regime change in Iran.

Mr. Trump chose a middle course, offering Israel as-yet undisclosed support from the U.S. intelligence community to carry out its attack and then turning up the pressure on Tehran to give immediate concessions at the negotiating table or face continued military onslaught.

Five days after Israel launched its attack, Mr. Trump’s posture continues to gyrate. The administration at first distanced itself from the strikes, then grew more publicly supportive as Israel’s initial military success became evident.

Now Mr. Trump is seriously considering sending American aircraft in to help refuel Israeli combat jets and to try to take out Iran’s deep-underground nuclear site at Fordo with 30,000-pound bombs — a step that would mark a stunning turnabout from his opposition just two months ago to any military action while there was still a chance of a diplomatic solution.

The story of what led up to the Israeli strike is one of two leaders in Mr. Trump and Mr. Netanyahu who share a common goal — preventing Iran from getting a nuclear bomb — but who are wary of each other’s motives. They speak often in public about their strong political and personal bonds, and yet the relationship has long been beset by mistrust.

Interviews with two dozen officials in the United States, Israel and the Persian Gulf region show how Mr. Trump vacillated for months over how and whether to contain Mr. Netanyahu’s impulses as he confronted the first foreign policy crisis of his second term. It was a situation he faced with a relatively inexperienced circle of advisers handpicked for loyalty.

This year he told a political ally that Mr. Netanyahu was trying to drag him into another Middle East war — the type of war he promised during his presidential campaign last year he would keep America out of.

But he also came to believe the Iranians were playing him in the diplomatic negotiations, much as President Vladimir V. Putin of Russia did as Mr. Trump sought a cease-fire and peace deal in Ukraine.

And when Israel chose war, Mr. Trump cycled from skepticism about attaching himself too closely to Mr. Netanyahu to inching toward joining him in dramatically escalating the conflict, even bucking the view that there is no immediate nuclear threat from Iran.

As he rushed back to Washington from a Group of 7 summit in Canada early on Tuesday morning, Mr. Trump took issue with an element of public testimony of Tulsi Gabbard, his director of national intelligence, that the intelligence community did not believe Iran was actively building nuclear weapons even as it enriches uranium that could ultimately be used for a nuclear arsenal. “I don’t care what she said,” Mr. Trump told reporters. “I think they were very close to having them.”

For Mr. Netanyahu, the last several months brought to an end years of trying to cajole the United States into backing or at least tolerating his long-held desire to deal Iran’s nuclear program a crippling blow. He appears to have judged, correctly, that Mr. Trump would ultimately come around, if only grudgingly.

Beyond the lives lost and destruction wrought, the crisis has also laid bare schisms within Mr. Trump’s party between those inclined to reflexively defend Israel, America’s closest ally in the region, and those determined to keep the United States from getting further mired in the Middle East’s cycle of violence.

In the middle was Mr. Trump, determined to block Iran’s path to a bomb and caught between cultivating his own image of strength and the potential strategic and political consequences of acting aggressively against Iran.

Asked for comment, a White House spokesman pointed to public comments made by Mr. Trump about not allowing Iran to obtain a nuclear weapon.

‘I Think We Might Have to Help Him’

When Mr. Trump met with his top advisers at the wooded presidential retreat of Camp David late on Sunday, June 8, to review the fast-evolving situation, the C.I.A. director, John Ratcliffe, provided a blunt assessment.

It was highly likely, he said, that Israel would soon strike Iran, with or without the United States, according to two people familiar with the briefing, who spoke on the condition of anonymity to describe a confidential discussion.

The president sat at the head of the table in a rustic conference room inside Laurel Lodge. There were no slides, only maps prepared by the chairman of the Joint Chiefs of Staff, Gen. Dan Caine. For two and a half hours, he and Mr. Ratcliffe described their expectation of an imminent Israeli attack. Ms. Gabbard was on National Guard duty that weekend and was not included in the meeting.

Mr. Trump’s advisers had been preparing for this moment. In late May, they had seen intelligence that made them concerned that Israel was going to move ahead with a major assault on Iran, regardless of what the president was trying to achieve diplomatically with Tehran.

Based on that intelligence, Vice President JD Vance and Marco Rubio, in his joint role as secretary of state and national security adviser, encouraged an effort to give the president a range of options so he could make quick decisions if necessary about the scope of American involvement.

Mr. Ratcliffe’s intelligence-gathering efforts went into overdrive. And in the two weeks leading up to the Camp David meeting, Mr. Trump’s top advisers met multiple times to get on the same page about what the menu of potential options might be.

The day after the Camp David meeting, Monday, June 9, Mr. Trump got on the phone with Mr. Netanyahu. The Israeli leader was unequivocal: The mission was a go.

Mr. Netanyahu laid out his intentions at a high level, according to three people with knowledge of the call. He made clear that Israel had forces on the ground inside Iran.

Mr. Trump was impressed by the ingenuity of the Israeli military planning. He made no commitments, but after he got off the call, he told advisers, “I think we might have to help him.”

Still, the president was torn over what to do next, and quizzed advisers throughout the week. He had wanted to manage Iran on his own terms, not Mr. Netanyahu’s, and he had professed confidence in his deal-making abilities. But he had come to believe that the Iranians were stringing him along.

Unlike some in the anti-interventionist wing of his party, Mr. Trump was never of the view that America could live with, and contain, an Iran with a nuclear bomb. He shared Mr. Netanyahu’s view that Iran was an existential threat to Israel. Mr. Netanyahu, he told aides, was going to do what was necessary to protect his country.

The Diplomatic Route

Israel had begun preparing in December for an attack on Iran, after the decimation of Hezbollah, an Iranian proxy, and the collapse of the Assad regime in Syria, opening up airspace for a bombing campaign.

Mr. Netanyahu made his first visit of the second Trump term to the White House on Feb. 4. He presented a gold-plated pager to Mr. Trump and a silver-plated pager to Mr. Vance — the same devices the Israelis had secretly packed with explosives and sold to unwitting Hezbollah operatives who would later be maimed and killed in a devastating remote-control attack on the Iran-backed Lebanese group. (Mr. Trump later told an ally he was disturbed by the gift.)

Mr. Netanyahu gave Mr. Trump a presentation about Iran in the Oval Office, walking him through images of the country’s various nuclear sites.

Israeli intelligence showed that Iran was making cruder and faster efforts to get to a nuclear weapon, and the weaker the Iranians got, the closer they moved to the bomb. In terms of the enrichment of uranium, Iran was days away from where it needed to be, but there were other components it required to complete the weapon.

The Israelis made an additional argument to Mr. Trump: If you want diplomacy to succeed you have to prepare for a strike, so there is real force behind the negotiations. Privately, they fretted that Mr. Trump would take what they viewed as an inadequate deal with Iran, similar to the 2015 deal negotiated by President Barack Obama, and that he would then declare mission accomplished. Mr. Netanyahu told Mr. Trump that the Iranians would be able to rebuild their air defenses that were destroyed during an Israeli attack in October, adding to the urgency.

After his election in November, Mr. Trump had named a close friend, Steve Witkoff, as his Middle East envoy, and gave him the job of trying to reach a deal with Iran. Mr. Trump, elected on a platform that promised to avoid military entanglements abroad, seemed to relish the idea of coming to a diplomatic resolution.

From the beginning of the administration, the Iranians were putting out feelers from a handful of countries to open a diplomatic path with the new administration. Then Mr. Trump made his own dramatic move: He sent a letter to Iran’s supreme leader, Ayatollah Ali Khamenei.

In early March, visitors to the Oval Office or guests on Air Force One were regaled by Mr. Trump about his “beautiful letter” to the ayatollah. One visitor treated to a live rendition recalled the letter’s basic message as: I don’t want war. I don’t want to blow you off the map. I want a deal.

Mr. Trump knew he was wading into dangerous political territory. More than perhaps any other subject, the Israel-Iran issue splits Mr. Trump’s coalition, pitting an anti-interventionist faction, led by media figures like the influential podcast host Tucker Carlson, against anti-Iran conservatives like the radio host Mark Levin.

But inside the administration, despite much hype about disagreements between “Iran hawks” and “doves,” ideological divisions were far less important than they were in Mr. Trump’s first term, when officials like Defense Secretary Jim Mattis and Secretary of State Rex Tillerson viewed the president as reckless and in need of being restrained from his impulses.

This time, nobody on Mr. Trump’s senior team played anything like that role. The new team generally supported Mr. Trump’s instincts and worked to carry them out. There were differences of opinion, to be sure, but few if any heated showdowns over Iran policy.

Mr. Rubio and Defense Secretary Pete Hegseth were always deferential to the president’s views, even if Mr. Hegseth, who has a close relationship with Mr. Netanyahu, was more trusting of the Israelis than some of his colleagues.

Mr. Vance warned repeatedly about the prospect of the United States getting entangled in a regime change war, but even those on the team who had historically supported a more muscular stance against Iran backed Mr. Witkoff’s diplomacy. Mr. Trump’s tough-on-Iran national security adviser at the time, Mike Waltz, nonetheless had a close working relationship with the more dovish Mr. Witkoff.

On the intelligence side, Mr. Ratcliffe delivered information without weighing in on one side or the other. And while everyone knew that Ms. Gabbard was as anti-interventionist as they come, she rarely pushed that view on the president.

In April, the Trump team began a series of negotiations in Oman, with the U.S. side of the talks led by Mr. Witkoff, along with Michael Anton, the director of policy planning at the State Department. By the end of May, the Trump team had delivered a written proposal to the Iranians.

It called for Iran to ultimately stop all enrichment of uranium and proposed the creation of a regional consortium to produce nuclear power that would potentially involve Iran, the United States and other Gulf states like Saudi Arabia and the United Arab Emirates.

Keeping Military Options

Even as Mr. Trump pursued a diplomatic solution, he seemed persuaded by one thing the Israelis had said to him: having credible military options would give him a stronger hand in negotiations with Iran.

Options for taking out Iran’s nuclear sites already existed inside the Pentagon, but after taking office in January the president authorized U.S. Central Command to coordinate with the Israelis on further refining and developing them.

By the middle of February, in coordination with the Israelis, Gen. Michael Erik Kurilla, the head of Central Command, had developed three main options. The first and most minimal was U.S. refueling and intelligence support for an Israeli mission. The second was Israeli and American joint strikes. The third was a U.S.-led mission with Israel in a supporting role. It would have involved American B-1 and B-2 bombers, carrier aircraft and cruise missiles launched from submarines.

There was also a fourth option, quickly discarded, that included, in addition to large-scale U.S. strikes, an Israeli commando raid with air support from American Osprey helicopters or other aircraft options.

But as Mr. Witkoff pursued negotiations with Tehran, mediated by Oman, the Israelis grew impatient.

Mr. Netanyahu made a quick visit to Mr. Trump at the White House in April. Among other requests, he asked for the American bunker-buster bomb to destroy the underground nuclear site at Fordo.

Mr. Trump, intent at the time on giving diplomacy a chance, was unpersuaded and in the days after the meeting, his team made a full-court press to stop the Israelis from launching pre-emptive strikes against Iran. The message from Mr. Trump’s team was blunt: You cannot just go and do this on your own. There are too many implications for us. These were tense conversations, but Mr. Trump’s advisers thought the Israelis had absorbed their message.

The president was concerned that Israel would strike out on its own or scuttle his diplomacy if Mr. Netanyahu did not like where his deal was heading. The Trump team also worried about what would happen if Israel launched strikes against Iran but failed to destroy all of its nuclear facilities.

But planning in Israel went ahead, driven in part by concern that Iran was rapidly building up its store of ballistic missiles that could be used for retaliatory attacks. Soon, U.S. intelligence agencies had amassed enough information to present it to Mr. Trump. The briefings got the president’s attention, and became the backdrop to the tense phone call in late May, during which Mr. Trump vented his unhappiness at Mr. Netanyahu.

Patience With Diplomacy Wears Thin

By that point, Mr. Vance was telling associates that he was worried about a potential regime change war, which he considered a dangerous escalation that could spiral out of control.

Mr. Vance had come to view a conflict between Israel and Iran as inevitable. The vice president was open to the possibility of supporting a targeted Israeli strike, but his concerns that it would grow into a more drawn-out war increased as the likely date of a strike approached, according to two people with knowledge of his thinking.

He turned his attention toward trying to keep America out of the conflict as much as possible beyond intelligence sharing. He worked closely with Mr. Trump’s inner circle, including Mr. Rubio, Mr. Hegseth and Susie Wiles, the White House chief of staff, to figure out contingency plans to protect American personnel in the region.

As May turned to June, Mr. Witkoff told colleagues that the United States and Iran were on the brink of a deal. But on Wednesday, June 4, Mr. Khamenei rejected the U.S. proposal. Mr. Trump was beginning to feel as if the Iranians were not serious about a deal, advisers said.

That same day, Mr. Levin, the conservative radio host, met with Mr. Trump and several of his advisers in the dining room adjoining the Oval Office. He had been an influential force in presenting an anti-Iran view to the president. The conversation with Mr. Levin appeared to have made an impression on the president, advisers said.

After that meeting, Mr. Trump told aides he wanted to give the deal talks a bit more of a chance. But his patience was wearing thin.

That Friday, his team scheduled a Sunday meeting in the privacy of Camp David.

A Rapid Change in Posture

Publicly, Mr. Trump was still stressing the importance of giving diplomacy a chance. And while doing so was not intended to deceive the Iranians about the immediacy of a potential attack from Israel, the possibility that it might keep Iran from going on heightened alert was a welcome side effect, a U.S. official involved in the discussions said.

But last Wednesday, there was no indication of any negotiated breakthrough, and by that point Mr. Trump’s inner circle knew the attack would start the next day.

In some private conversations, Mr. Trump questioned the wisdom of the Israeli decision to attack. “I don’t know about Bibi,” he told one associate, adding that he had warned him against the strikes.

Mr. Trump joined his national security team in the White House Situation Room on Thursday evening as the first wave of strikes was unfolding, and was still keeping his options open. Earlier that day he was telling advisers and allies that he still wanted to get a deal with Iran.

The first official statement from the administration after the strikes came not from Mr. Trump but from Mr. Rubio, who distanced the United States from the Israeli campaign and made no mention of standing by an ally, even though the U.S. intelligence community was already providing support.

But as the night wore on and the Israelis landed a spectacular series of precision strikes against Iranian military leaders and strategic sites, Mr. Trump began to change his mind about his public posture.

When he woke on Friday morning, his favorite TV channel, Fox News, was broadcasting wall-to-wall imagery of what it was portraying as Israel’s military genius. And Mr. Trump could not resist claiming some credit for himself.

In phone calls with reporters, Mr. Trump began hinting that he had played a bigger behind-the-scenes role in the war than people realized. Privately, he told some confidants that he was now leaning toward a more serious escalation: going along with Israel’s earlier request that the United States deliver powerful bunker-busting bombs to destroy Iran’s nuclear facility at Fordo.

As recently as Monday, Mr. Trump held out the possibility that Mr. Witkoff or even Mr. Vance could meet with Iranian officials to seek a negotiated deal. But as Mr. Trump abruptly left the Group of 7 summit in Canada to rush back to Washington, there was little indication that the conflict would be brought to a quick end through diplomacy.

Helene Cooper, Julian E. Barnes and Eric Schmitt contributed reporting.

It said that it issued its updated assessment on the basis of continued analysis of high resolution satellite imagery. The I.A.E.A. also said that there was still no evidence of damage at Iran’s nuclear plant near the city of Isfahan or at Fordo, a facility hidden in a mountain in the northwest of the country.

The extent to which Iran’s nuclear facilities were degraded was a critical issue in the assault that Prime Minister Benjamin Netanyahu of Israel launched on Friday. Israel wants to force the government in Tehran to abandon its well-established nuclear program.

Mr. Netanyahu said last week that the nuclear program was an existential threat to his country, but Tehran maintains that it is solely for peaceful purposes and has given no hint that it would shut its atomic industry. Decades-long efforts to keep Iran from developing nuclear weapons have yielded uneven results.

President Trump said on Monday that Iran wanted to make a deal over its nuclear program, and the country’s foreign minister, Abbas Araghchi, signaled an openness to resuming talks with U.S. representatives about curtailing its nuclear development program. However, it remains unclear whether a diplomatic resolution is likely.

Iran has launched deadly waves of missiles and drones at Israel in retaliation for Israel’s campaign, which has killed Iranian nuclear scientists as well as military commanders and civilians.

Last week, the I.A.E.A. said that Iran was not complying with its nuclear nonproliferation obligations, the first time the agency had passed a resolution against the country in 20 years.

Iran has taken steps over the years to shield its nuclear industry from the possibility of Israeli attacks. The main site for uranium enrichment is at Natanz, which is roughly 140 miles south of Tehran. Other sites include Fordo; Isfahan; Parchin, a military complex southeast of Tehran where Iran has tested high explosives; and Bushehr, which is on the coast of the Persian Gulf.

Israeli airspace has been closed for commercial flights since Friday morning, and roughly 100,000 to 150,000 Israelis who left the country before its surprise attack on Iran have been stranded overseas. Regularly scheduled El Al flights will be canceled until at least Monday, the airline said.

It was unclear when people who were visiting Israel when the strikes began would be able to leave the country. Citing a “government decision,” El Al said there were no outbound passenger flights from Israel to international destinations at the moment.

About 38,000 tourists are currently in Israel, the Israeli Ministry of Tourism said on Tuesday. It said it would be opening a service to help them register for outbound flights, but did not specify when those flights would depart or how many passengers they would be able to take. The tourism ministry also suggested that visitors could use land border crossings to Jordan and Egypt to leave, though the Israeli National Security Council has advised Israeli citizens not to use those crossings to return home because of security risks.

In addition to the Israelis who are expected to return home via El Al, some stranded Israeli tourists will be returning to Israel from Cyprus via a cruise ship operated by the Israeli cruise company Mano Maritime. The company said a ship would leave Limassol, Cyprus, on Thursday.

The Times of Israel, citing a statement from Mano Maritime, said the ship could carry 2,000 passengers and that after the first trip, the ship would return to Limassol to pick up more Israelis. The journey, which The Times of Israel said would be run in coordination with Israel’s transportation ministry, takes about 16 hours each way. Mano Maritime did not respond to a request for comment.

Some Israeli travelers are considering remaining abroad for now, given that there are few signs the fighting will end soon. Civilian casualties are rising in both Iran and Israel, where 24 people have died and about 600 were injured. Israeli strikes in Iran have killed more than 200 people and injured 1,400.

Anushka Patil contributed reporting.