Iran is assessing damage to its nuclear industry and arrangements had been made for its restoration, Iran's nuclear chief Mohammad Eslami said, according to Mehr news, after a series of Israeli and US strikes targeted Iran's main nuclear facilities.
"The plan is to prevent interruptions in the process of production and services," Mr Eslami said.
It comes after US President Donald Trump said a ceasefire between Israel and Iran was now in place and asked both countries not to violate it, only hours after Iran launched waves of missiles, which Israel's ambulance service said killed four people.
"THE CEASEFIRE IS NOW IN EFFECT. PLEASE DO NOT VIOLATE IT!" Mr Trump said in a Truth Social post.
When he announced last night what he called a complete ceasefire to end a 12-day war, he appeared to suggest that Israel and Iran would have time to complete missions that were under way, at which point the ceasefire would begin in a staged process.
He said the truce would begin at around 5am Irish time, with Iran unilaterally halting all operations first and that Israel would follow suit 12 hours later.
Witnesses said they heard explosions near Tel Aviv and Beersheba in southern Israel before Mr Trump's statement.
Israel's military said six waves of missiles were launched by Iran and Israel's national ambulance service said four people were killed in Beersheba, the first reported deaths in Israel since Mr Trump announced the ceasefire.
Iran's semi-official SNN news agency reported that Tehran fired its last round of missiles before the ceasefire came into effect.
Iranian media also said an overnight Israeli strike on the north of the country killed nine people, ahead of Mr Trump's announcement of the start of a ceasefire.
"Four residential buildings were completely destroyed and several neighbouring houses were damaged in the blasts," said Fars news agency, citing an official in the northern province of Gilan.
A senior White House official said Mr Trump had brokered a ceasefire deal in a call with Israeli Prime Minister Benjamin Netanyahu and Israel had agreed so long as Iran did not launch further attacks.
"On the assumption that everything works as it should, which it will, I would like to congratulate both Countries, Israel and Iran, on having the Stamina, Courage, and Intelligence to end, what should be called, 'THE 12 DAY WAR'," Mr Trump wrote on Truth Social.
An Iranian official earlier confirmed that Tehran had agreed to a ceasefire, but the country's foreign minister said there would be no cessation of hostilities unless Israel stopped its attacks.
Abbas Araqchi said early this morning that if Israel stopped its "illegal aggression" against the Iranian people no later than 4am Tehran time (1.30am Irish time), Iran had no intention of continuing its response afterwards.
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"The final decision on the cessation of our military operations will be made later," Mr Araqchi added in a post on X.
Israel, joined by the United States at the weekend, has carried out attacks on Iran's nuclear facilities, after alleging Tehran was getting close to obtaining a nuclear weapon.
Iran denies ever having a nuclear weapons programme but Supreme leader Ayatollah Ali Khamenei has said that if it wanted to, world leaders "wouldn't be able to stop us".
Israel, which is not a party to the international Non-Proliferation Treaty, is the only country in the Middle East believed to have nuclear weapons. Israel does not deny or confirm that.
Watch: Israeli emergency workers search for survivors after missile strike
Qatar's Prime Minister Sheikh Mohammed bin Abdulrahman Al Thani secured Tehran's agreement during a call with Iranian officials, an official briefed on the negotiations said.
US Vice President JD Vance, Secretary of State Marco Rubio and US special envoy Steve Witkoff were in direct and indirect contact with the Iranians, a White House official said.
Hours earlier, three Israeli officials had signalled Israel was looking to wrap up its campaign in Iran soon and had passed the message on to the United States.
Mr Netanyahu had told government ministers whose discussions ended early this morning not to speak publicly, Israel's Channel12 television reported.
Watch: JD Vance says Iran now incapable of building a nuclear weapon
Earlier yesterday, Mr Trump said he would encourage Israel to proceed towards peace after dismissing Iran's attack on a US air base in Qatar that caused no injuries and thanking Tehran for the early notice of the strikes.
He said Iran fired 14 missiles at the base, calling it "a very weak response, which we expected, and have very effectively countered."
Iran's handling of the attack recalled earlier clashes with the United States and Israel, with Tehran seeking a balance between saving face with a military response but without provoking a cycle of escalation it cannot afford.
Iran's attack came after US bombers dropped bunker-buster bombs on Iranian underground nuclear facilities at the weekend, joining Israel's air war.
Much of Tehran's population of 10 million has fled after days of bombing.
The Trump administration maintains that its aim was solely to destroy Iran's nuclear programme, not to open a wider war.
"Iran was very close to having a nuclear weapon," Mr Vance said in an interview on Fox News.
"Now Iran is incapable of building a nuclear weapon with the equipment they have because we destroyed it," he said.
Mr Trump has cited intelligence reports that Iran was close to building a nuclear weapon, without elaborating.
However, US intelligence agencies said earlier this year they assessed that Iran was not building a nuclear weapon and a source with access to US intelligence reports said last week that that assessment had not changed.
In a social media post on Sunday, Mr Trump spoke of toppling the hardline clerical rulers who have been Washington's principal foes in the Middle East since Iran's 1979 Islamic Revolution.
Israel, however, had made clear that its strikes on Evin prison - a notorious jail for housing political prisoners - and other targets in Tehran were intended to hit the Iranian ruling apparatus broadly, and its ability to sustain power.
