US President Donald Trump took a gamble by inserting the US into the worsening conflict between Israel and Iran, but it may have paid off - at least for now.

Trump announced on Monday evening that the two countries had agreed to a ceasefire that he said could lead to a lasting peace.

If the American president has in fact ended what he labelled the "12 Day War", it would make for a significant step back from the brink of a conflict that seemed on the verge of engulfing the region, along with pulling America further in after US airstrikes hit Iranian nuclear facilities on Saturday.

"Provided that the Israeli regime stops its illegal aggression against the Iranian people no later than 4 am Tehran time," Iranian Foreign Minister Abbas Araghchi said in a statement, "we have no intention to continue our response afterwards."

The Israeli government later said it agreed to the proposal after "achieving the objectives" of its attacks on Iran.

The two parties appeared to be on the verge of turning down the heat as the 04:00 (00:30 GMT) deadline arrived in Tehran, and the Israeli attacks reportedly came to a halt.

But the fragility of the agreement was on full display just two hours later, when Israel's defence minister accused Iran of violating the ceasefire and vowed to respond forcefully. Iran, meanwhile, denied any violation.

The Trump administration will no doubt be hoping this is a blip, owing to the obvious tensions, and the ceasefire is ultimately respected by both sides.

Trump's ceasefire announcement came after a tumultuous day in the region, when Iran followed through on its promise to retaliate for Saturday's US strike.

According to early reports, all the Iranian missiles directed at the massive US base in Qatar were intercepted and there were no American casualties or damage.

During his address to the nation on Saturday night, President Trump warned that there would be an overwhelming American answer to any Iranian attacks on US interests. He promised that there were more targets that could be struck by American forces if needed.

For more than 24 hours, the world waited to see what Iran would do. Once Iran had acted, attention swung back to the US president and, after a few hours, he had his first say.

"Iran has officially responded to our Obliteration of their Nuclear Facilities with a very weak response, which we expected, and have very effectively countered," Trump posted on his social media site.

He said that Iran had "gotten it all out of their 'system'", and added that "perhaps Iran can now proceed to Peace and Harmony in the Region".

While the damage is reported to limited, Trump seemed inclined to hold his fire in the hope that the Iranians would be willing to negotiate in earnest. And, behind the scenes, the White House says he was talking to Qatari mediators and Israeli Prime Minister Benjamin Netanyahu to work out the details of the ceasefire.

Trump's weekend attack on Iran was a high-risk manoeuvre, but a scenario in which the pay-offs are already coming into view.

A similar dynamic played itself out in January 2020, when Trump ordered the targeted killing of Iranian Revolutionary Guard leader Qasem Soleimani in Baghdad.

Iran launched missiles at military bases in Iraq, injuring more than 100 American soldiers, but the US chose not to escalate. Cooler heads ultimately prevailed.

According to US media, in their latest attack on Monday, Iran fired a number of missiles at American bases equal to the total number of bombs US warplanes dropped during its weekend attack.

That, along with the advance notice Iran provided to the Qatari government prior to the launch, for which Trump said he was grateful, suggests the Iranians are seeking proportionality, not escalation.

For most of the day, Trump was more focused on the price of oil, American media coverage and a suggestion by former Russian President Dimitry Medvedev that an outside nation provide Iran with nuclear weapons.

US officials have stated that this president follows through on his threats, in contrast with some of his predecessors.

If Iran were to launch another round of attacks - and there were American deaths or significant damage - pressure would mount for Trump to respond.

For the moment, however, he is seemingly eyeing an off-ramp to more fighting and both countries appear willing to entertain it.