Speculation is mounting of a US strike on Iran as military resources are deployed into position.
More than 40 extra jets are said to have been sent to the UK and Europe by Donald Trump in recent days.
They are thought to include stealth bombers and air-to-air refuellers – which could be critical for any operation in the Middle East.
The movements have raised expectations that action is imminent, after Mr Trump denied he was interested in securing a ceasefire between Israel and Iran and told residents to evacuate Tehran.
Instead he has stressed the importance of stopping Iran from getting nuclear weapons, and cut short his attendance at the G7 summit in Canada to return to Washington.
A joint statement with fellow leaders stopped short of calling for de-escalation in the immediate conflict – although it did support easing tensions in the region more broadly.
However, Keir Starmer played down the prospect of the US getting involved in the clashes this evening.
‘There is nothing the President said that suggests he’s about to get involved in this conflict, on the contrary, the G7 statement was about de-escalation,’ he told reporters at the summit.
He ominously revealed his exit was for a ‘much bigger’ reason than a ceasefire as he is set to convene the National Security Council in the White House.
‘Publicity seeking President Emmanuel Macron, of France, mistakenly said that I left the G7 Summit, in Canada, to go back to D.C. to work on a ‘ceasefire’ between Israel and Iran,’ Mr Trump wrote.
‘Wrong! He has no idea why I am now on my way to Washington, but it certainly has nothing to do with a Cease Fire. Much bigger than that. Whether purposely or not, Emmanuel always gets it wrong. Stay Tuned!’
Mr Macron had seemed to indicate such a deal was on the table when he spoke to reporters at the summit.
‘There is indeed an offer to meet and exchange. An offer was made especially to get a ceasefire and to then kick-start broader discussions. We have to see now whether the sides will follow.’
He added optimistically that ‘if the United States can achieve a ceasefire, that’s a very good thing’.
The communique issued by the G7 leaders carefully avoided saying that the immediate standoff with Iran should be ‘de-escalated’.
‘We affirm that Israel has a right to defend itself. We reiterate our support for the security of Israel,’ it said.
‘We also affirm the importance of the protection of civilians.
‘Iran is the principal source of regional instability and terror.
‘We have been consistently clear that Iran can never have a nuclear weapon.
‘We urge that the resolution of the Iranian crisis leads to a broader de-escalation of hostilities in the Middle East, including a ceasefire in Gaza.’
Sir Keir told reporters: ‘On nuclear, Iran’s nuclear programme, I’ve been very clear. We are deeply concerned about the programme. I certainly do not want Iran to have a nuclear weapon.
‘But the thrust of the statement is in accordance with what I was saying on the way out here, which is to de-escalate the situation, and to de-escalate it across the region rather than to escalate it.’
US Defence Secretary Pete Hegseth has announced ‘the deployment of additional capabilities’ to the Middle East.
Air-to-air refuellers, F-22 Raptors and F-35 Lightning jets are among the assets that have been crossing the Atlantic, according to the Sun.
The USS Nimitz aircraft carrier is also en route to the region.
Mr Trump headed back to DC as Israel warned hundreds of thousands of people to evacuate the middle of Iran’s capital as Israel’s air campaign on Tehran appeared to broaden on the fourth day of an intensifying conflict.
Yesterday Israel’s military issued an evacuation warning to 330,000 people in a part of central Tehran that houses the country’s state TV and police headquarters, as well as three large hospitals, including one owned by Iran’s paramilitary Revolutionary Guard.
Mr Trump himself seemed to co-sign the warning in a Truth Social post.
‘Iran should have signed the ‘deal’ I told them to sign. What a shame, and waste of human life. Simply stated, IRAN CAN NOT HAVE A NUCLEAR WEAPON. I said it over and over again! Everyone should immediately evacuate Tehran!’
The city, one of the region’s largest, is home to around 9.5 million people.
Israel’s military has issued similar evacuation warnings for civilians in parts of Gaza and Lebanon ahead of strikes.
The IDF says its sweeping assault on Iran´s top military leaders, nuclear scientists, uranium enrichment sites and ballistic missile program is necessary to prevent its longtime adversary from getting any closer to building an atomic weapon.
The strikes have killed at least 224 people since Friday.
Iran has retaliated by launching more than 370 missiles and hundreds of drones at Israel.