More fighter jets are being sent to the Middle East, Sir Keir Starmer has said after Iran threatened to target UK, French and US bases if the countries help stop strikes on Israel.
The Prime Minister said further military assets are being deployed to provide “contingency support” across the region amid escalating hostilities between the two long-time foes.
Additional refuelling aircraft have been deployed from UK bases and more fighter jets will be sent over, it is understood.
Crews began deployment preparations on Friday morning, when it was clear the situation in the region was deteriorating, a spokesperson for the prime minister said.
The UK already has RAF jets in the Middle East as part of Operation Shader.
Speaking to reporters travelling with him on a visit to Canada, Sir Keir declined to rule out intervening in the conflict entirely but made clear he would continue pressing for de-escalation and said the “intense” developments over the weekend would be discussed in detail at the G7 summit.
Sir Keir said: “Our constant message is de-escalate, and therefore everything we’re doing, all discussions we’re having are to do with de-escalation.”
Asked whether he would rule out UK involvement, he said: “I’m not going to get in to that.”
It comes hours after Iran warned Israel’s allies, including the UK, that it will target their regional military bases if they help shoot down Iranian missiles, the country’s state media reported.
Iran has vowed to avenge Friday's Israeli onslaught, which gutted Iran's nuclear and military leadership and damaged atomic plants and military bases, killing 78 people including civilians, according to Iran's UN envoy.
Tehran warned the US, the UK and France not to help Israel stop Tehran's retaliatory strikes, according to Reuters news agency.
The Israeli attack is believed to be the most significant Iran has faced since its war with Iraq in the 1980s. Nuclear sites were bombed and commanders and scientists were killed in a stated bid to stop Iran from building an atomic weapon.
Israeli Prime Minister Benjamin Netanyahu said on Saturday that Israel's strikes have set Iran's nuclear program back, possibly by years, and that heavier blows were yet to come.
"We will hit every site and every target of the Ayatollahs' regime and what they have felt so far is nothing compared with what they will be handed in the coming days," Netanyahu said in a video message. He added that the military was now destroying Iran's ability to manufacture ballistic missiles.
Israel further attacked Iran on Saturday, and appeared to have hit its oil and gas industry for the first time, with Iranian state media reporting a blaze at a gas field.
Iranian state TV also reported on Friday that around 60 people, including 20 children, had been killed in an attack on a housing complex. Israel said it had attacked more than 150 targets.
Host Oman confirmed on Saturday that the next round of nuclear talks between the US and Iran in Washington had been scrapped. Iranian Foreign Minister Abbas Araqchi said holding talks was unjustifiable while Israel's "barbarous" attacks were ongoing.
Iran had launched its own retaliatory missile volley on Friday night. Air raid sirens sent residents into shelters in Israel as waves of missiles streaked across the sky and interceptors rose to meet them, killing at least three people. An Israeli official said Iran had fired around 200 ballistic missiles in four waves.
Tensions rose further as US President Donald Trump lauded Israel’s strikes and warned of much worse to come unless Iran quickly accepts the sharp downgrading of its nuclear programme.
Israel has said its operation could last weeks, and urged Iran's people to rise up against their Islamic clerical rulers.
Iranian fire still struck residential districts in Israel and Defence Minister Israel Katz said Iran's leadership had crossed a red line, threatening that “Tehran will burn” if further missiles are fired.
At least one Iranian missile appeared to bypass the Iron Dome missile system in Tel Aviv as a plume of smoke rose from the city. Air raid sirens sounded out across Israel and its citizens were ordered to move into bomb shelters, as the attack began.
The United States, Israel's main ally, helped shoot down Iranian missiles, two US officials said.
The rocket attacks on the Tel Aviv area wounded 34 people, according to Israel's paramedic service, including one woman critically injured after being trapped under rubble.
Israel's paramedic service said two people were killed and another 19 people were injured after Iranian missiles struck the central Israeli city of Rishon LeZion on Saturday. Emergency services rescued a baby girl trapped in a house hit by a missile in the area, police said.
Video showed teams searching through the rubble of one home.
A spokesperson for Beilinson Hospital said one woman was killed in a second Iranian barrage when a building was hit in Tel Aviv.
Calls from Sir Keir Starmer and other world leaders for calm amid the mounting conflict appeared to fall on deaf ears, as Tehran struck back against Israel's attacks.
A spokesman for Iran's Foreign Ministry said continuing nuclear talks with the US would be “meaningless” after the strikes, although he stopped short of saying the talks were cancelled according to The Mizan news agency.
Operation Rising Lion - the offensive against Tehran - has mainly targeted nuclear sites, including destroying the above ground section of Iran's main Natanz nuclear base.
At least 20 Iranian military commanders were said to have been killed. Iran also said six of its top nuclear scientists had been killed.
Among the generals killed on Friday were the armed forces chief of staff, Major General Mohammad Bagheri, and the Revolutionary Guards chief, Hossein Salami.
Major General Mohammad Pakpour, promoted to replace Salami as Guards commander, vowed retaliation in a letter to the Supreme Leader read on state television: “The gates of hell will open to the child-killing regime.”
Israel's Prime Minister Benjamin Netanyahu said “more is on the way” in a video message released on Friday night.
On Friday, Israel's western allies attempted a diplomatic blitz aimed at cooling temperatures in the Middle East.
After convening a Cobra meeting of senior ministers and officials, Prime Minister Sir Keir Starmer spoke to Mr Netanyahu, urging him to de-escalate and work towards a “diplomatic resolution”.
And Sir Keir joined with France's Emmanuel Macron and Germany's Friedrich Merz in calling for restraint.
David Lammy, the Foreign Secretary, spoke to Iran's foreign minister and urged calm, later warning the Middle East is facing a “moment of grave peril”.
Both the UK and the US have insisted they were not involved in the Israeli strikes and that Israel acted unilaterally.
The first time Israel discussed the strikes with the UK was at midday on Friday, according to Tzipi Hotovely, the country's ambassador to the UK.
