General Qassem Soleimani, the head of Tehran’s elite Quds Force who spearheaded military operations in the Middle East, was targeted in an attack at Baghdad’s international airport on Friday.
Foreign Secretary Dominic Raab discussed the dramatic ratcheting of tensions with Donald Trump’s Secretary of State Mike Pompeo later in the day.
But there was criticism of the US for apparently not giving warning of the attack to the UK, which has hundreds of troops deployed in Iraq.
Outgoing Labour leader Jeremy Corbyn described the strike as an “assassination” and called for the Government to stand up to the “belligerent actions” from the US.
The US President said Gen Soleimani was targeted because he was “plotting to kill” many Americans and that he “should have been taken out many years ago”.
Iran’s Supreme Leader Ayatollah Ali Khamenei warned that “severe revenge awaits the criminals” behind the strike and announced three days of national mourning.
Mr Raab issued a statement saying the Government had “always recognised the aggressive threat posed by the Iranian Quds force” led by the general.
“Following his death, we urge all parties to de-escalate. Further conflict is in none of our interests,” Mr Raab added.
The Secretary of State thanked Mr Raab in a phone call for recognising the “aggressive threats posed” by the Quds Force in his statement, according to US spokeswoman Morgan Ortagus.
Mr Pompeo was also said to have stressed that the White House “remains committed to de-escalation”.
The president did not tone down his rhetoric, however, and later tweeted: “He should have been taken out many years ago!”
Prime Minister Boris Johnson, who has been celebrating the new year on the private Caribbean island of Mustique, is yet to comment and Number 10 would not discuss his travel plans.
Prominent Tory MP Tom Tugendhat, who was chairman of the Foreign Affairs Committee in the last Parliament, was critical of the US for not giving the UK warning of the attack, though the Government did not confirm it was not briefed in advance.
He urged the White House to “share much more closely with allies” in the future, adding to the BBC that “the purpose of having allies is that we can surprise our enemies and not each other”.
The Ministry of Defence said there are around 400 British troops deployed in Iraq as part of the UK’s fight against the Islamic State terror group.
A further 500 personnel are based at RAF Akrotiri in Cyprus which flies fast jets and reconnaissance planes over Iraq and Syria, the MoD added.
Mr Corbyn said “the US assassination” of the general “is an extremely serious and dangerous escalation of conflict in the Middle East with global significance”.
“The UK Government should urge restraint on the part of both Iran and the US, and stand up to the belligerent actions and rhetoric coming from the United States,” the MP added.
“All countries in the region and beyond should seek to ratchet down the tensions to avoid deepening conflict, which can only bring further misery to the region, 17 years on from the disastrous invasion of Iraq.”
Emily Thornberry, the shadow foreign secretary bidding to become the next Labour leader, criticised the PM for having “pathetically unopposed” Mr Trump’s decision to pull out of the Iran nuclear deal.
“The Foreign Office’s call for restraint today is too little and far too late, in the wake of such a brazen, unlawful and provocative attack,” she added.
Other potential Labour leaders also weighed in on the attack, with shadow Brexit secretary Sir Keir Starmer calling it an “extremely serious situation” and urged the UK to “engage, not isolate Iran”.
Tory MP Tobias Ellwood, a former defence minister who served as a captain in the Army, tweeted “this is big”, adding: “Expect repercussions.”
Dr Jack Watling, a research fellow at the Royal United Services Institute defence think tank, said Iran would strike back but would take care not to provoke a “full-scale conflict”.
And he said that British citizens could face capture or arrest in the region if the UK was seen by Iran to be working with the US in the situation.
“The Iranians do not draw a direct line between the UK and US. However, if the UK is perceived to be participating in US actions then they will directly target UK interests,” Dr Watling said.
The Foreign Office advises British-Iranian dual nationals against all travel to Iran and for other British nationals to seek the department’s advice before travelling to the nation.
British nationals risk being arbitrarily detained or arrested by Tehran, the department warns.
Nazanin Zaghari-Ratcliffe has been among the dual nationals being held in Iran since she was arrested in 2016 and accused of spying while visiting family.
Her husband Richard Ratcliffe told ITV’s Good Morning Britain: “I sit here partly worried for what that means for Nazanin, partly worried what that means for my in-laws, sat in their ordinary living room in Tehran where they’re all really worried.”