(BSS/AFP) - US President Donald Trump announced Monday that Iran and Israel had agreed to a staggered ceasefire that would bring about an "official end" to their conflict, as strikes continued to hammer Tehran overnight.

"It has been fully agreed by and between Israel and Iran that there will be a Complete and Total CEASEFIRE," Trump wrote on his Truth Social platform.

There was however no immediate confirmation from either of the Middle Eastern adversaries, whose unprecedented exchange of attacks has seen hundreds killed in Iran and two dozen in Israel.

Trump said the ceasefire would be a phased 24-hour process beginning at around 0400 GMT Tuesday, with Iran unilaterally halting all operations. Israel would follow suit 12 hours later, the president said.

"Upon the 24th hour, an official end to the 12-day war will be saluted by the world," he said, adding that both sides had agreed to remain "peaceful and respectful" during each phase of the process.

Explosions nonetheless continued to rock Tehran overnight, with explosions in the north and center of the Iranian capital described by AFP journalists as some of the strongest since the conflict broke out.

Any cessation in hostilities would come as a huge relief to world leaders frantic about an escalation in violence igniting into a wider conflagration.

The adversaries had been swapping missile fire since Israel carried out surprise "preemptive" strikes against Iran on June 13, targeting nuclear and military sites, and prompting Trump to warn of a possible "massive" regional conflict.

- Strikes on US base -
The US leader`s ceasefire announcement came hours after Iran launched missiles at the largest US military facility in the Middle East -- Al Udeid Air Base in Qatar -- in a move Trump shrugged off as "very weak."

Calling for a de-escalation, Trump said Tehran had given advance notice of the barrage. No one had been hurt in the attack, Trump said.

Iran`s National Security Council confirmed having targeted the base "in response to the US aggressive and insolent action against Iran`s nuclear sites and facilities."

But it added that the number of missiles launched "was the same as the number of bombs that the US had used" -- a signal that it had calibrated its response to be directly proportional rather than escalatory.

"This was calibrated and telegraphed in a way that would not result in any American casualties, so that there is an off ramp for both sides," Ali Vaez, a senior advisor at the International Crisis Group, told AFP.

The offensive came after the United States joined its ally Israel`s military campaign against Iran, attacking an underground uranium enrichment center with massive bunker-busting bombs and hitting two other nuclear facilities overnight Saturday into Sunday.

As international concern mounted that Israel`s campaign and the US strikes could ignite into a wider conflict, French President Emmanuel Macron insisted that "the spiral of chaos must end" while China warned of the potential economic fallout.

- `Blatant aggression` -
Iran said its assault in Qatar wasn`t targeting the Middle Eastern neighbor, but the government in Doha accused Tehran of "blatant aggression" and claimed its right to a "proportional" response.

Iran`s state media quoted the Revolutionary Guard Corps announcing that six missiles had hit Al Udeid, which had been evacuated beforehand, according to the Qataris.

The broadside was made up of "short-range and medium-range ballistic missiles," a US defense official said.

AFP reporters heard blasts in central Doha and in Lusail, north of the capital, on Monday evening, and saw projectiles moving across the night sky.

Iranians gathered in central Tehran to celebrate, images on state TV showed, with some waving the flag of the Islamic republic and chanting "Death to America."

Qatar earlier announced the temporary closure of its airspace in light of "developments in the region," while the US embassy and other foreign missions warned their citizens to shelter in place.

Israeli strikes on Iran have killed more than 400 people, Iran`s health ministry has said. Twenty-four people have died in Iran`s attacks on Israel, according to official figures.

After a day of tit-for-tat missile launches between Israel and Iran, the Israeli army called around midnight for residents in part of central Tehran to evacuate, saying it was "targeting the Iranian regime`s military infrastructure."