Tel Aviv. The US military struck three sites in Iran early Sunday, inserting itself into Israel’s war aimed at destroying the country’s nuclear program in a risky gambit to weaken a longtime foe amid Tehran’s threat of reprisals that could spark a wider regional conflict.

President Donald Trump said Iran’s key nuclear sites were “completely and fully obliterated,” and he warned Iran against carrying out retaliatory attacks, saying the United States could hit more targets “with precision, speed and skill.”

“There will either be peace or there will be tragedy for Iran, far greater than we have witnessed over the last eight days,” Trump said in an address to the nation from the White House.

The Atomic Energy Organization of Iran confirmed that attacks took place on its Fordo, Isfahan, and Natanz sites, but it insisted that its work will not be stopped.

The decision to directly involve the US in the war comes after more than a week of strikes by Israel on Iran that aimed to systematically eradicate the country’s air defenses and offensive missile capabilities, while damaging its nuclear enrichment facilities. But US and Israeli officials have said that American stealth bombers and the 30,000-pound (13,500-kilogram) bunker buster bomb they alone can carry offered the best chance of destroying heavily fortified sites connected to the Iranian nuclear program buried deep underground.

“We have completed our very successful attack on the three Nuclear sites in Iran, including Fordow, Natanz, and Esfahan," Trump said in a post on social media. "All planes are now outside of Iran air airspace. A full payload of BOMBS was dropped on the primary site, Fordow. All planes are safely on their way home.”

Trump added in a later post: “This is an HISTORIC MOMENT FOR THE UNITED STATES OF AMERICA, ISRAEL, AND THE WORLD. IRAN MUST NOW AGREE TO END THIS WAR. THANK YOU!”

Israeli Prime Minister Benjamin Netanyahu praised Trump's decision to attack in a video message directed at the American president.

“Your bold decision to target Iran’s nuclear facilities, with the awesome and righteous might of the United States, will change history,” he said. Netanyahu said the US “has done what no other country on earth could do.”

The White House and Pentagon did not immediately elaborate on the operation. But Fox News host Sean Hannity said shortly after 9 p.m. Eastern that he had spoken with Trump and that six bunker buster bombs were used on the Fordo facility. Hannity said 30 Tomahawk missiles fired by US submarines 400 miles away struck the Iranian nuclear sites of Natanz and Isfahan.

The strikes are a perilous decision, as Iran has pledged to retaliate if the US joined the Israeli assault, and for Trump personally. He won the White House on the promise of keeping America out of costly foreign conflicts and scoffed at the value of American interventionism.

UN Secretary-General Antonio Guterres said that he was “gravely alarmed” by the “dangerous escalation” of American strikes.

“There is a growing risk that this conflict could rapidly get out of control -- with catastrophic consequences for civilians, the region, and the world,” he said in a statement.

Trump told reporters Friday that he was not interested in sending ground forces into Iran, saying it’s “the last thing you want to do.” He had previously indicated that he would make a final choice over the course of two weeks.

Iran’s Supreme Leader Ayatollah Ali Khamenei warned the United States on Wednesday that strikes targeting the Islamic Republic will “result in irreparable damage for them.” And Iranian Foreign Ministry spokesman Esmail Baghaei declared “any American intervention would be a recipe for an all-out war in the region."

Trump has vowed that he would not allow Iran to obtain a nuclear weapon, and he had initially hoped that the threat of force would bring the country’s leaders to give up its nuclear program peacefully.

The Israeli military said Saturday it was preparing for the possibility of a lengthy war, while Iran’s foreign minister warned before the US attack that American military involvement “would be very, very dangerous for everyone.”

The prospect of a wider war loomed. Iranian-backed Houthi rebels in Yemen said they would resume attacks on US vessels in the Red Sea if the Trump administration joined Israel’s military campaign. The Houthis paused such attacks in May under a deal with the US.

The US ambassador to Israel announced that the U.S. had begun “assisted departure flights,” the first from Israel since the Hamas-led attack on Oct. 7, 2023, that sparked the war in Gaza.

White House press secretary Karoline Leavitt said Thursday that Trump planned to make his decision on the strikes within two weeks. Instead, he struck just two days later.

Trump appears to have made the calculation -- at the prodding of Israeli officials and many Republican lawmakers -- that Israel’s operation had softened the ground and presented a perhaps unparalleled opportunity to set back Iran’s nuclear program, perhaps permanently.

The Israelis say their offensive has already crippled Iran’s air defenses, allowing them to already significantly degrade multiple Iranian nuclear sites.

But to destroy the Fordo nuclear fuel enrichment plant, Israel appealed to Trump for the bunker-busting American bomb known as the GBU-57 Massive Ordnance Penetrator, which uses its weight and sheer kinetic force to reach deeply buried targets and then explode. The bomb is currently delivered only by the B-2 stealth bomber, which is only found in the American arsenal.

If deployed in the attack, it would be the first combat use of the weapon.

The bomb carries a conventional warhead, and is believed to be able to penetrate about 200 feet (61 meters) below the surface before exploding, and the bombs can be dropped one after another, effectively drilling deeper and deeper with each successive blast.

The International Atomic Energy Agency has confirmed that Iran is producing highly enriched uranium at Fordo, raising the possibility that nuclear material could be released into the area if the GBU-57 A/B were used to hit the facility.

Previous Israeli strikes at another Iranian nuclear site, Natanz, on a centrifuge site have caused contamination only at the site itself, not the surrounding area, the IAEA has said.

Trump’s decision for direct U.S. military intervention comes after his administration made an unsuccessful two-month push -- including with high-level, direct negotiations with the Iranians -- aimed at persuading Tehran to curb its nuclear program.

For months, Trump said he was dedicated to a diplomatic push to persuade Iran to give up its nuclear ambitions. And he twice -- in April and again in late May -- persuaded Netanyahu to hold off on military action against Iran and give diplomacy more time.

The US in recent days has been shifting military aircraft and warships into and around the Middle East to protect Israel and US bases from Iranian attacks.

All the while, Trump has gone from publicly expressing hope that the moment could be a “second chance” for Iran to make a deal to delivering explicit threats on Khamenei and making calls for Tehran’s unconditional surrender.

“We know exactly where the so-called ‘Supreme Leader’ is hiding,” Trump said in a social media posting. “He is an easy target, but is safe there - We are not going to take him out (kill!), at least not for now.”