The US military has struck three sites in Iran, President Donald Trump says, directly joining Israel's effort to decapitate the country's nuclear program.
The risky gambit to weaken a longtime foe comes amid Tehran's threat of reprisals that could spark a wider regional conflict.
The decision to directly involve the US comes after more than a week of strikes by Israel on Iran that have moved to systematically eradicate the country's air defences and offensive missile capabilities, while damaging its nuclear enrichment facilities.
But US and Israeli officials have said that American stealth bombers and a 30,000-lb. 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 space. A full payload of BOMBS was dropped on the primary site, Fordow. All planes are safely on their way home."
The strikes are a perilous decision for the US as Iran has pledged to retaliate if it joins the Israeli assault, and for Trump personally, having won the White House on the promise of keeping America out of costly foreign conflicts and scoffed at the value of American interventionism.
Two US officials on Saturday told Reuters B-2 bombers were being deployed to the Pacific Island of Guam as Trump weighed whether the US should take part in Israel's strikes against Iran.
While they did not disclose details on numbers of B-2s, which can carry weapons designed to destroy targets deep underground, one of the officials said no orders had yet been given to move the aircraft beyond Guam.
Israeli military officials said they had completed another series of strikes in southwest Iran, having targeted dozens of military targets.
Iran's Foreign Minister Abbas Araqchi met UK, French and German counterparts, plus the European Union, on Friday in Geneva in search of a path back to diplomacy and a possible ceasefire.
Proposals made by the European countries, however, were "unrealistic," the senior Iranian official told Reuters, saying that insistence on them would not bring agreement closer.
"In any case, Iran will review the European proposals in Tehran and present its responses in the next meeting," the official said, adding that zero enrichment was a dead end and Iran would not negotiate over its defensive capabilities.
Israel launched attacks on June 13, saying Iran was on the verge of developing nuclear weapons, while Iran says its atomic program is only for peaceful purposes.
Israel is widely assumed to possess nuclear weapons, which it neither confirms nor denies.
At least 430 people have been killed and 3500 injured in Iran since Israel began its attacks, Iranian state-run Nour News said, citing the health ministry.
In Israel, 24 civilians have been killed by Iranian missile attacks, according to local authorities, in the worst conflict between the longtime enemies.
More than 450 Iranian missiles have been fired towards Israel, according to the Israeli prime minister's office.
Israeli officials said 1272 people have been injured since the beginning of the hostilities, with 14 in serious condition.
At a meeting of the Organisation of Islamic Co-operation (OIC) in Istanbul, Araqchi said Israel's aggression, which he said had indications of US involvement, should stop so Iran can "come back to diplomacy".
"It is obvious that I can't go to negotiations with the US when our people are under bombardments under the support of the US," he told reporters on the sidelines, before meeting Turkish President Tayyip Erdogan.
The top Iranian diplomat said US involvement in the conflict would be "very dangerous".
US President Donald Trump had said he would take up to two weeks to decide whether the US should enter the conflict on Israel's side.
Gulf Co-operation Council ambassadors expressed concerns to United Nations nuclear watchdog chief Rafael Grossi about the safety of nuclear facilities close to their countries and "dangerous repercussions" of targeting them, Qatar state news agency said.
Israel said it was attacking military infrastructure.
with AP