The U.N.’s nuclear watchdog says the war could lead to ‘unimaginable levels’ of destruction.

As the damage from the latest strikes was still becoming clear, world leaders called on both sides to ease their attacks, even as President Trump’s decision to join Israel’s campaign against Iranian nuclear sites raised fears that the war would escalate. American military and intelligence officials detected potential signs that Iran-backed militias were preparing to attack American bases in Iraq, and possibly Syria.

Iranian officials appeared to be weighing their options for retaliation against the United States. Iran’s foreign minister, Abbas Araghchi, met with President Vladimir V. Putin of Russia on Monday as the Kremlin seemingly sought to push back against the suggestion that it was offering little support to Iran. Even though Russia is a longtime ally of Iran, there has been little sign so far that Moscow is prepared to provide military assistance to Tehran in this war.

More than 24 hours after U.S. bombers hit three uranium-enrichment sites in Iran, prompting Mr. Trump to declare that Iran’s nuclear program had been “totally obliterated,” the actual state of the program seemed far more murky, with senior officials conceding they did not know the fate of Iran’s stockpile of near-bomb-grade uranium. On Monday, the Israeli military also said it had struck access routes to the Fordo site in order to obstruct them.

Trump administration officials emphasized on Sunday that the United States did not want an all-out war with Tehran, but Mr. Trump’s position was less clear — particularly when he raised the prospect of regime change in Iran in a social media post on Sunday. He was set to meet with his National Security Council on Monday.

Here’s what else to know:

• Calls for peace: After European foreign ministers met to discuss Iran, the European Union’s chief diplomat, Kaja Kallas, said that “the concerns of retaliation and this war escalating are huge.” The International Atomic Energy Agency held an emergency meeting in Vienna, where the head of the agency, Rafael Grossi, warned that “violence and destruction could reach unimaginable levels” if Iran, Israel and the United States do not find a path to diplomacy.

• Possible response: Mr. Trump’s decision to attack Iran seemed likely to dim hopes for a negotiated solution to end the fighting, only days after the president had indicated he would wait for as long as two weeks to give diplomacy a chance. While U.S. officials say that Iran has depleted its stockpile of medium-range missiles, the country still has an ample supply of other weapons, including rockets and drones.

• The strikes: Pentagon officials described a tightly choreographed operation that included B-2 bombers carrying 30,000-pound bunker-buster bombs and submarine-fired Tomahawk cruise missiles hitting a trio of sites in less than a half-hour. A senior U.S. official acknowledged that the attack on Fordo had not destroyed the heavily fortified site, but it had been severely damaged.

• Economic impact: Asian markets dipped on Monday, reflecting investor concern over possible economic fallout from the U.S. strikes and any potential moves by Iran to disrupt shipping through the Strait of Hormuz, a critical transit point for global oil supplies.

River Akira Davis contributed reporting.

“We may not agree on the reasons behind and even the consequences of the current crisis, but there is a common denominator that exists,” he said at the meeting of the watchdog, the International Atomic Energy Agency. “First, we don’t want to see a nuclear accident.”

Israel began its military campaign against Iran’s nuclear program and military leadership on June 13. The United States intervened militarily early on Sunday local time, attacking the three Iranian nuclear sites, with President Trump saying that the goal was to prevent Iran from building a nuclear weapon.

American officials have said that while Israel’s intelligence agency believes that Iran can achieve a nuclear weapon in 15 days, American spy agencies believe that it could take several months, and up to a year, for Iran to make a weapon.

The International Atomic Energy Agency declared on June 12 that Iran was not complying with its nuclear nonproliferation obligations. But Mr. Grossi stressed on Monday that the correct approach was diplomacy, and urged a return to negotiations.

“Military escalation not only threatens lives, it also delays us from taking the diplomatic path to achieve the long-term assurance that Iran does not acquire a nuclear weapon,” Mr. Grossi said Monday. Iran insists that its nuclear program is for civilian use, not to develop weapons.

“There has never been a time more important than now to muster the political courage to step away from the edge,” Mr. Grossi said.

Later on Monday, the Israeli military said that it had attacked access routes to the Fordo nuclear enrichment site to obstruct them, a day after the United States struck the site itself. Both Israeli and American officials have said the site was severely damaged in Sunday’s U.S. strikes, but that it would take time for a full damage assessment.

Mr. Grossi said that at this time “no one, including the I.A.E.A.,” is in a position to has fully assessed the damage at Fordo. He added that Iran has informed the agency that there was no increase in off-site radiation levels at any of the three sites hit by the United States.

Senior American officials have conceded that they do not know the fate of Iran’s stockpile of near-bomb-grade uranium. Mr. Grossi said on Monday that Iran’s foreign minister, Abbas Araghchi, had written in a June 13 letter to him that Iran would adopt “special measures” to protect nuclear equipment and materials.

Aaron Boxerman contributed reporting.

In the original post, according to a screenshot by the local TV news station KTLA, the department said “Our hearts go out to the victims and the families impacted by the recent bombings in Iran.”

In its statement on Sunday, the Sheriff’s Department called that post “offensive and inappropriate.”

“This post was unacceptable,” the Sheriff’s Department said, “made in error, and does not reflect the views of Sheriff Robert G. Luna or the Department.”

As a law enforcement agency, the Sheriff’s Department said, it did not comment on “foreign policy or military matters.” It said it was conducting an internal investigation to determine how the post was created and published.

Los Angeles County is home to a large Iranian population, as well as a large Jewish population.

Of the roughly 400,000 Iranian-born immigrants in the United States, roughly one-third lives in or around Los Angeles, according to the Migration Policy Institute. Westwood, a neighborhood on the west side of Los Angeles near the U.C.L.A. campus, has been nicknamed “Tehrangeles.”

Los Angeles is also home to more than 500,000 Jews, the second-largest Jewish community in the U.S., according to 2021 research by Brandeis University. Roughly half of the Jewish households in Los Angeles include an immigrant to the United States, including many from Iran.

The Sheriff’s Department’s social media post emphasized that there was no specific danger for residents but encouraged people to be vigilant.

“At the moment, there are no known threats to Los Angeles County. However, out of an abundance of caution, we are increasing patrol checks at places of worship and other sensitive locations throughout the county,” the sheriff’s department said.

“Ministers are very much focused on the diplomatic solution, and also the concerns of retaliation and this war escalating are huge,” Kaja Kallas, the European Union’s top diplomat, told journalists. Ms. Kallas added that any Iranian closure of the Strait of Hormuz, a key shipping route for oil and gas, would be “extremely dangerous.”

American military and intelligence officials have detected signs that Iran-backed militias were preparing to attack American bases in Iraq, and possibly in Syria, in retaliation for the U.S. strikes in Iran on Sunday, fueling fears that tensions could ramp up. If Tehran were to close access to the Strait of Hormuz, oil prices could soar and some U.S. Navy ships could be pinned in the Persian Gulf, American military officials say.

Ms. Kallas and foreign ministers from Britain, France, and Germany met with Iran’s foreign minister, Abbas Araghchi, in Geneva on Friday. Ms. Kallas said that at that meeting, Iran was opening up to discussions of “nuclear, but also broader security issues that are concerning Europe.”

Still, officials fretted that a peaceful outcome remained far from guaranteed.

“We are very concerned about the risk of an escalation, which could be devastating in the Middle East and have very serious consequences for the stability of the world,” Jean-Noël Barrot, France’s minister for Europe and foreign affairs, said as he headed into Monday’s meeting.

“Europe can bring its experience, its competence, in-depth knowledge of these questions to open a space for negotiation,” he added.

While Mr. Barrot and other European officials suggested that strikes on Iranian nuclear facilities by Israel and the United States might delay nuclear developments, they also said that a negotiated solution would be more durable in the long run.

“At this moment, I think it’s very important to find a way back to the negotiations,” Caspar Veldkamp, the Dutch minister for foreign affairs, told reporters.

Videos verified by the New York Times showed an explosion today at the entrance to Evin Prison, a notorious detention facility on the outskirts of Tehran where hundreds of dissidents and political prisoners are held. Footage shows the moment of the blast at an entrance into the prison compound, and large clouds of smoke emanating from a metal gate below a sign that reads ‘Evin Detention Facility’ in Farsi. Another video, distributed by the Iranian broadcaster Iran International, is filmed from a car driving on the highway directly adjacent to the compound and shows plumes of smoke continuing to rise from the area.

Iranian news outlets reported that Israeli strikes hit a building beside to the Red Crescent Society in the capital Tehran. A video posted by the government-affiliated Mehr news agency, verified by the New York Times, showed white smoke billowing up in front of the building.

Saying that “military escalation not only threatens lives, it also delays us from taking the diplomatic path to achieve the long term assurance that Iran does not acquire a nuclear weapon,” Grossi also offered to travel immediately to Iran and to engage with all parties involved to help ensure the protection of nuclear facilities.

In more than a week of fighting between Israel and Iran, Israel’s military has steered clear of hitting Iranian naval assets. So while Iran’s ability to respond to attacks has been severely damaged, it has a robust navy and maintains operatives across the region, where the United States has more than 40,000 troops. Iran also has an array of mines that its navy could lay in the Strait of Hormuz, which hugs a portion of Iran’s southern border.

A quarter of the world’s oil and 20 percent of the world’s liquefied natural gas passes through the Strait of Hormuz, so mining the choke point would cause oil and gas prices to soar. The majority of those fuels go to Asia, meaning that countries there would most likely be severely affected by any closure. The United States and other countries would feel the effects in the form of higher energy costs.

Closing the waterway could isolate American minesweepers in the Persian Gulf on one side of the strait. Two defense officials indicated that the Navy was looking to disperse its ships in the gulf so that they would be less vulnerable. A Navy official declined to comment, citing operational security. The officials spoke on condition of anonymity because they were not authorized to speak publicly.

Even before the U.S. military struck Iranian nuclear sites over the weekend, Iran vowed that it would respond forcefully to any attack by American forces — potentially setting off a cycle of escalation. Since the strikes, Iran appears to be weighing its options.

“Iran is strategically weaker but operationally still lethal across the region, and Americans still have troops across that part of the world,” said Brian Katulis, a senior fellow at the Middle East Institute.

Military officials and analysts said missile and drone attacks remained the biggest retaliatory threat to U.S. bases and facilities in the region. Some also worry that the Quds Force, a shadowy arm of Iran’s military, could attack U.S. troops.

Much is at stake for Iran if it decides to retaliate. “Many of Iran’s options are the strategic equivalent of a suicide bombing,” said Karim Sadjadpour, an Iran policy expert at the Carnegie Endowment for International Peace. “They can do enormous damage to others if they mine the Strait of Hormuz, destroy regional oil facilities and rain a missile barrage against Israel, but they may not survive the blowback.”

But Iran can make it hugely expensive, and dangerous, for the U.S. Navy to have to conduct what would most likely be a weekslong mine-clearing operation in the Strait of Hormuz, according to one former naval officer who was stationed on a minesweeper in the Persian Gulf. He and other Navy officers said that clearing the strait could also put American sailors directly in harm’s way.

Mining the strait would also inflict severe economic damage in Iran because nearly all of the country’s oil exports move through the channel.

In the battle for global narratives, China has long cast the United States as a warmonger and a destabilizing power while presenting itself as a responsible global leader championing peace and fairness.

At an emergency meeting of the Security Council on Sunday, Mr. Fu said that China condemned the U.S. strikes and was joining Russia and Pakistan in drafting a U.N. resolution calling for a cease-fire, the safety of civilians and a start to peace negotiations.

The criticism of the United States was echoed in Chinese state media reports on Monday, with the official news agency, Xinhua, accusing the United States of escalating violence in the region.

“The worsening situation in the Middle East is a stark reminder that power politics and military interventions lead to nothing but chaos and instability,” the article said.

In a separate editorial on Monday, the Communist Party tabloid, the Global Times, said the U.S. strikes had weakened “the foundation of the international security order.”

On China’s heavily censored internet forums, users have left furious comments about how Iran was deceived into thinking it was negotiating a nuclear agreement with the United States, only to lower its guard and become the target of U.S. bombs.

China’s rhetoric belies a more complicated reality. Beijing has been one of Tehran’s biggest backers, diplomatically and economically. Its purchases of almost all of Iran’s oil exports have helped a brutal Iranian regime stay in power and deliver support to its terrorist proxies abroad, including Hamas, Hezbollah and the Houthis.

It remains to be seen how China might use its influence over Iran as fears of a broader conflict grow. Secretary of State Marco Rubio on Sunday urged China to persuade Tehran not to make good on a threat to close the Strait of Hormuz, one of the world’s most vital waterways for the transport of oil.

“China will certainly oppose Iran” closing the strait, said Wang Yiwei, the director of the Institute of International Affairs at Renmin University in Beijing, because of China’s need for access to Iranian oil. But it would only do so on its terms and in its own time, he suggested.

“However, it would be improper, or even counterproductive, to discuss this with the United States, or to exert pressure on Iran at the request of the United States,” he added.

When asked on Monday what China would do if Iran closed the strait, Guo Jiakun, a spokesman for the Foreign Ministry, deflected and called on the international community to “step up its efforts to promote the de-escalation of the conflict.”

Sirens are now wailing in central Israel in response to additional missile fire, according to the Israeli military.

Israeli fighter jets attacked surface-to-surface missile launchers and storage sites in Kermanshah, the military later said, calling it part of Israel’s broader aim of degrading Iran’s military capabilities.

The price of West Texas Intermediate, the benchmark for U.S. crude oil, was up roughly 1 percent, paring some of their increases. Gold, a traditional safe-haven asset, also rose. Futures contracts for the S&P 500, indicating how the index might perform when markets open in New York, were up slightly.

Traders were waiting for clearer indications of whether there would be an escalation in conflicts in the Middle East — particularly any moves by Iran that might disrupt oil shipments through the Strait of Hormuz.

The Strait of Hormuz is a critical transit point for global oil supplies. Last year, about 20 million barrels of oil were shipped through the waterway each day, representing about 20 percent of the world’s total supply. Most of that oil was bound for Asia.

Places like Japan and Taiwan rely on the Middle East for almost all of their crude oil imports, meaning that any disruption to traffic through the passageway could inflict a large economic blow. China is the largest purchaser of Iranian oil.

Oil prices, hovering around $76 a barrel, are expected to reach $80, but if the risk of Iran blocking the Strait of Hormuz increases, so will the price of oil, said Takahide Kiuchi, executive economist at Nomura Research Institute. In that case, “the Japanese economy could be exposed to downside risks that exceed those of the Trump tariffs,” he said.

Other analysts expect fallout from the U.S. strikes to be relatively short-lived.

The oil market is better equipped to respond to shocks than it has been in the past because of spare capacity held by exporters, according to Daniel Hynes, a senior commodity strategist at ANZ Research. Geopolitical events involving producers can have a big impact on oil markets, but in recent years, prices have tended to quickly retreat as risks ease, Mr. Hynes said.

Daniel Ives, an analyst at Wedbush Securities, said there could be more volatility in stock movements this week. But, he said, the market may view the Iran threat as “now gone.” In that case, he said, “the worst is now in the rearview mirror.”

Joe Rennison contributed reporting from New York.

One day after the administration announced it had carried out airstrikes at three nuclear sites in Iran, the mood in some communities around military bases on U.S. soil varied from firm support to bitter disagreement. But one sentiment stood out among those interviewed: concern for the safety of America’s troops everywhere.

No one knows how the strikes on Iran could affect service members. Pete Hegseth, the secretary of defense, emphasized on Sunday that the administration did not want an open-ended war. But Iranian leaders have vowed to retaliate, and U.S. military installations in the Middle East, with more than 40,000 active-duty troops and civilians employed by the Pentagon, are already potential targets.

That reality, along with the potential repercussions for the entire military, was on the minds of many people around U.S. bases at home, even as service members accepted that reality as part of the job.

“A lot of the families around here are quickly realizing this is a real threat; this is something we need to be worried about,” said Meghan Gilles, 37, a self-described military brat who works in the Army Reserve’s human resources division at Fort Campbell in Kentucky, a training site and home to the 101st Airborne Division.

At Eglin Air Force Base in Florida, Blake Carlson, a 23-year-old Army National Guard combat medic who was visiting from Austin, Texas, said that he could be deployed. “It’s what I signed up for,” he said. “If I have to, I’ll do it.” But his mother and brother hoped the country would not be dragged into the escalating conflict in the Middle East.

Some people who were interviewed stood by Mr. Trump and agreed with his assertions that the targeted bombings were unlikely to lead to a wider conflict. Mr. Carlson’s mother, Tonya Carlson, said she hoped the attack would force Iran to negotiate with the United States.

Others stood by Mr. Trump’s statement that Iran posed an imminent threat — a point that contradicts recent national security assessments. “Iran doesn’t need to have nuclear weapons, for sure,” said Tony Saluzzo, 72, a former combat engineer who served in the U.S. offensive against Iraq and lives near Fort Campbell.

James Arthur, a 42-year-old retired Coast Guard captain who lives north of Tampa, Fla., and was visiting the Air Force Armament Museum at the Eglin base, said that the Iran airstrikes happened “about two decades too late.”

Other former service members castigated Mr. Trump for bombing Iran without congressional approval. The Constitution’s framers included language to ensure that wars would not be entered rashly, said Paul Oyler, a Navy veteran who served in Iraq and Afghanistan and who lives near the Naval Air Station Lemoore in California, where he was based while on active duty.

He said he would have agreed with the airstrikes if there were a proven, credible threat to the region, but “I don’t have any reason to believe that Iran was in possession of actual nuclear weapons.”

Denver Thiery, 30, who works on military maintenance contracts and lives in Trenton, Ky., near Fort Campbell, said he would remain firmly behind Mr. Trump. But he also acknowledged that it was difficult to know exactly what capabilities Iran possessed.

“I don’t know the truth of what’s going on,” he said. “I don’t know if they really have nuclear warheads or not. I don’t know what I can support anymore.”

Ms. Gilles, the reservist, whose father is a veteran and whose husband is an active-duty serviceman, was troubled by the decision to edge the country to war at the very moment the government was cutting funding for Veterans Affairs.

The administration is taking away a lot of benefits for veterans and “then just sending them off again to be the world police,” Ms. Gilles said.

If the current conflict worsens, military members and veterans said, they would put aside their disagreements over Mr. Trump and support one another. But one veteran lamented what he said such a scenario would ultimately mean.

“I learned from my time on active duty that war is devastating,” Mr. Oyler said.

John Ismay contributed reporting.

The Iranians have made it clear they are not interested in having conversations with the United States, accusing Washington of deceiving Tehran during the last set of negotiations while planning the air attack. Moreover, that stockpile of fuel is now one of the few nuclear bargaining chips in Iranian hands.

In a briefing for reporters on Sunday, Defense Secretary Pete Hegseth and the new chairman of the Joint Chiefs of Staff, Dan Caine, avoided Mr. Trump’s maximalist claims of success. They said an initial battle-damage assessment of all three sites struck by Air Force B-2 bombers and Navy Tomahawk missiles showed “severe damage and destruction.”

Satellite photographs of the primary target, the Fordo uranium enrichment plant that Iran built under a mountain, showed several holes where a dozen 30,000-pound Massive Ordnance Penetrators — one of the largest conventional bombs in the U.S. arsenal — punched deep holes in the rock. The Israeli military’s initial analysis concluded that the site, the target of American and Israeli military planners for more than 26 years, sustained serious damage from the strike but had not been completely destroyed.

But there was also evidence, according to two Israeli officials with knowledge of the intelligence, that Iran had moved equipment and uranium from the site in recent days. And there was growing evidence that the Iranians, attuned to Mr. Trump’s repeated threats to take military action, had removed 400 kilograms, or roughly 880 pounds, of uranium enriched to 60 percent purity. That is just below the 90 percent that is usually used in nuclear weapons.

The 60-percent enriched fuel had been stored deep inside another nuclear complex, near the ancient capital of Isfahan. Rafael Mariano Grossi, the director general of the International Atomic Energy Agency, said by text that the fuel had last been seen by his teams of United Nations inspectors about a week before Israel began its attacks on Iran. In an interview on CNN on Sunday he added that “Iran has made no secret that they have protected this material.”

Asked by text later in the day whether he meant that the fuel stockpile — which is stored in special casks small enough to fit in the trunks of about 10 cars — had been moved, he replied, “I do.” That appeared to be the mystery about the fuel’s fate that Mr. Vance was discussing.

If so, Isfahan would not be the only place where the custodians of the Iranian nuclear program — a subject of nationalistic pride and the symbol of Iran’s ability to defend itself — were trying to move equipment and material out of sight, and harden the Fordo plant to protect what had to stay in place.

Satellite images released by Maxar Technologies at the tunnels leading into the Fordo mountain, taken in the days before the American strike, show 16 cargo trucks positioned near an entrance. An analysis by the Open Source Centre in London suggested that Iran may have been preparing the site for a strike.

It is unclear exactly what, if anything, was removed from the facility.

In fact, there was only so much the Iranians could save. The giant centrifuges that spin at supersonic speeds, purifying uranium, are piped together and bolted to the cement floor. One U.S. official said it would have been unrealistic to completely move equipment out of Fordo after the conflict with Israel began.

The official added that historical documents about the nuclear program were buried in the bowels of the site, likely complicating any efforts in reconstituting it. In coming days, both the Iranians and intelligence agencies expect to learn more about the Natanz enrichment site, which is older, larger and less well protected than Fordo. It was struck by the Israelis repeatedly, and they destroyed an aboveground enrichment center and disrupted the electrical system. Mr. Grossi later said he believed the interruption of the electrical supply could have sent the centrifuges spinning out of control, probably destroying all of them.

How long it would take the Iranians to repair and replace that equipment is unknown; it would probably stretch for years. But Iran is also building a new, deep replacement for Natanz in the south of the city. Officials in Tehran have told the I.A.E. A. that they have not yet opened the plant, so there is nothing to see.

If Iran is truly pursuing a nuclear weapon — which it officially denies — it is taking more time than any nuclear-armed nation in history. The United States developed the Manhattan Project in four years or so, developing the bombs dropped at Hiroshima and Nagasaki to end the war in the Pacific. The Soviet Union conducted its first test in 1949, only four years later. India, Pakistan and Israel all sped the process.

The Iranians have been at it for more than 20 years, and an archive of data stolen from a Tehran warehouse by Israel a number of years ago showed that Iranian engineers were exploring nuclear triggers and other equipment that would only be used to detonate a weapon. That was around 2003, when, according to American intelligence, the engineers received instructions to halt work on weaponization.

Comments by Mr. Trump and Prime Minister Benjamin Netanyahu in recent days suggest they believe that work has resumed, though no evidence to support the contention has been made public. If so, the strikes on Fordo, Natanz and Isfahan may only reinforce the view among Iranian leaders that they need a weapon for survival of the government.

History also suggests that diplomacy has usually been more effective than sabotage or military attacks in providing assurances that a country does not pursue atomic weapons. More than 15 years ago, the joint U.S.- Israeli attack on Natanz, using a sophisticated cyber weapon, caused about a fifth of the country’s 5,000 or so centrifuges to blow up.

But the Iranians not only rebuilt, they installed more sophisticated equipment. Before Israel’s attack this month, they had roughly 19,000 centrifuges in operation.

It was only when the Obama administration struck the 2015 nuclear deal with Iran that the United States got a fuller picture of its capabilities, thanks to the work of inspectors. And those inspections were choked off — and many security cameras disabled — after Mr. Trump declared the nuclear accord a “disaster” and withdrew from it.

Tehran’s reaction was to scale up centrifuge production, enrich uranium at levels only weapons states need, and stonewall the I.A.E.A.

Now, it is unclear whether the team of I.A.E.A. inspectors who were in the country when the conflict with Israel broke out will be permitted by the Iranian government to resume their inspections, which would include verifying the whereabouts and the safety of that near-bomb-grade uranium.

All international inspections have been suspended during wartime, Iranian officials have said. And even if they were to resume, it was unclear the inspectors could physically gain access to the bombed Fordo underground plant, or the wreckage of the larger enrichment facility at Natanz.

Mick Mulroy, a former Pentagon official in the first Trump administration and a former C.I.A. officer, said of the strike: “With the type and amount of munitions used, it will likely set back the Iranian nuclear weapon program two to five years.”