Iran vowed to defend itself after the United States military joined Israel’s war against Iran early Sunday morning by dropping bombs and firing missiles at three key nuclear sites in the country. The strikes prompted fears of more dangerous escalations across the Middle East.

President Trump said the objective was the “destruction of Iran’s nuclear enrichment capacity.” He claimed success, saying in a brief, televised address from the White House that the nuclear facilities had been “completely and totally obliterated.” The full extent of the damage to the sites was not immediately clear.

“Iran, the bully of the Middle East, must now make peace,” Mr. Trump said. “If they do not, future attacks will be far greater and a lot easier.”

Iranian officials said they were working to assess the scale of the damage to its facilities at Fordo, Natanz and Isfahan. In a news conference on Sunday morning, the chairman of the Joint Chiefs of Staff, Gen. Dan Caine, said that the initial battle damage assessment indicated that all three sites sustained “severe damage and destruction” and that it was too soon to say whether Iran still retains some nuclear ability.

Mr. Trump’s decision to attack Iran was likely to dim hopes for a negotiated solution to end the fighting, just days after the president had indicated he would wait for as long as two weeks to give diplomacy a chance. After the U.S. strikes early on Sunday local time, Iran’s foreign minister, Abbas Araghchi lashed out at the United States for undercutting recent diplomatic efforts — and rejected calls by European leaders to return to the negotiating table.

“How can Iran return to something it never left, let alone blew up?” Mr. Araghchi wrote on social media. He later told a news conference in Istanbul that Iran “reserves all options to defend its security interests and people,” but declined to be more specific — including about whether Iran would retaliate against U.S. military bases in the Middle East or move to close the Strait of Hormuz, a key global shipping lane beside southern Iran.

“We have to respond based on our legitimate right of self-defense,” he told reporters, adding that “there are a variety of options available to us.”

The U.S. strikes ushered in a period of high alert in the region, where more than 40,000 American troops are on bases and warships, as the Pentagon braced for almost-certain retaliation. 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.

Hours after the American bombs were dropped, Iran launched a new round of missiles toward Israel, triggering air raid sirens across the country and sending millions of people scrambling for shelter. The Israeli authorities said that at least 16 people were wounded in the barrage, one of many exchanges of fire between the two sides since Israel’s military launched a surprise assault on Iran on June 13.

The nuclear sites attacked by the U.S. include Iran’s two major uranium enrichment centers: the heavily fortified mountain facility at Fordo and a larger enrichment plant at Natanz that Israel had struck several days ago with smaller weapons. Prime Minister Benjamin Netanyahu said early Sunday that the U.S. strikes had been carried out “in full coordination” between the American and Israeli militaries.

Here’s what you need to know:

  • Potential damage: New satellite imagery taken shortly after the strikes at Fordo reveals damage and likely entry holes for the American “bunker-buster” bombs. The imagery, captured by Planet Labs, shows distinct changes in the ground’s appearance and gray dust near the potential strike locations. Iranian officials acknowledged the attacks, and the International Atomic Energy Agency said it had not detected any increases in radiation outside the sites. Mahdi Mohammadi, a senior adviser to the speaker of Iran’s Parliament, said on social media that Fordo had been evacuated beforehand and that damage there was “not irreversible.”

  • International reaction: America’s allies and adversaries were scrambling on Sunday to process the U.S. strikes on three nuclear sites in Iran that brought the U.S. military directly into Israel’s war. Mr. Araghchi said he plans to meet with President Vladimir V. Putin of Russia, a key ally, on Monday. As fears grew that the attacks could further escalate tensions across the Middle East, some officials condemned the strikes while others urged calm. Read more ›

  • Reaction in Congress: Top Republicans rallied behind Mr. Trump, calling the strikes a necessary check on Iran’s nuclear ambitions. But senior Democrats and some Republican lawmakers condemned the move as unconstitutional and said that it could drag the United States into a broader war. Read more ›

  • Strike details: Pentagon officials shared new details on Sunday morning about the strikes. General Caine said at the news conference that they involved 75 precision-guided munitions, including 14 of the Pentagon’s 30,000-pound bunker buster bombs, and that a Navy submarine in the Persian Gulf fired two dozen Tomahawk missiles as part of the attack. A U.S. official earlier said that six B-2 bombers dropped a dozen bunker buster bombs on the Fordo nuclear site, and Navy submarines fired 30 TLAM cruise missiles at Natanz and another nuclear site in Isfahan. One B-2 also dropped two bunker busters on Natanz, according to the official, who spoke on the condition of anonymity to discuss military operations. The strikes marked the first time the U.S. Air Force had ever used such bombs in combat.

  • What’s next? Now that Mr. Trump has helped Israel, it will most likely initiate a more dangerous phase in the war. Here are some ways that could play out, and a look at how the U.S. military’s powerful bunker-busting bombs work.

Reporting was contributed by David E. Sanger, Robert Jimison, Michael Gold, Megan Mineiro, Jonathan Swan, Aaron Boxerman Yan Zhuang and Talya Minsberg.

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