The US has said it is not involved in Israel's bombardment of Iranian nuclear sites, an escalation that is threatening to send the region deeper into conflict.

Secretary of State Marco Rubio released a statement soon after the strikes began, saying Israel had taken "unilateral action" and warning Iran not to retaliate against the US.

"We are not involved in strikes against Iran, and our top priority is protecting American forces in the region," Rubio said. "Let me be clear: Iran should not target U.S. interests or personnel."

While the US has so far publicly distanced itself from the Israeli operation, Iranian state TV was quick to point the finger at Washington, accusing it of being "complicit" in an attack that has "killed children".

The Israeli strikes - dubbed Operation Rising Lion - targeted Iran's nuclear programme and other military sites, according to a statement by the Israel Defence Force.

Israeli Prime Minister Benjamin Netanyahu said the attack was necessary due to Iran's continued movement to "weaponise" enriched uranium and was critical to "Israel's very survival".

Israel has declared a state of emergency and said the country expects retaliation. Netanyahu said the strikes against Iran would "continue for as many days as it takes".

Israeli officials reportedly notified the US before beginning the strikes, according to Israeli public broadcaster Kan.

Rubio's statement said Israel had advised the US that they believed this action was necessary for its self defence.

"President Trump and the administration have taken all necessary steps to protect our forces and remain in close contact with our regional partners."

Worried that an attack by Israel could provoke Iran to retaliate by targeting US military installations nearby, the US had already partially evacuated US embassy staff from Iraq.

The State Department had also limited the movement of its employees within Israel to the Tel Aviv area, as well, according to a social media post on Thursday.

Earlier on Thursday, President Donald Trump had warned that a military operation against Iran would "blow" the negotiations his administration has been holding with Iran in a bid to curb its nuclear programme.

News of the Israeli strikes came just moments after the president left a picnic held for members of Congress at the White House, in which he gave no indication of anything happening.

Trump has for some time been working to negotiate with Iran over limiting its nuclear programme, but a deal has so far been out of reach.

"As long as I think there will be an agreement, I don't want them going in," Trump said of an Israeli strike earlier on Thursday, adding he would "love to avoid a conflict".

During the same event, Trump said that he did not want to describe any Israeli action as "imminent", he said that "it looks like something could well happen."

Trump has repeatedly expressed dissatisfaction with the progress of negotiations, and on Thursday said that the Iranians "are going to have to give us some things that they're not willing to give us right now."

Hours after he made those remarks - and just before the Israeli airstrikes - however, he posted on social media that the US remained committed to a "diplomatic resolution to the Iran nuclear issue" and that the "entire administration" had been directed to negotiate with Iran".

The president's Middle East envoy Steve Witkoff was due to hold another round of talks with Iranian officials on Sunday.

On Friday morning, Trump was scheduled to meet with his National Security Council behind closed doors in the Situation Room, the White House announced late on Thursday.