No 10 has urged Iraq to allow UK troops to stay in the country following the US assassination of Iranian general Qasem Soleimani, saying their work is vital.
Soleimani was killed in a US drone strike in Iraq on Friday on the orders of President Donald Trump.
Iraqi MPs responded to the strike by passing a non-binding resolution calling for an end to the foreign military presence in their country.
European leaders have called for all sides to show restraint.
Boris Johnson will chair a meeting of senior ministers later to discuss the deepening crisis and will speak to his Iraqi counterpart by phone.
About 400 British troops are stationed in Iraq, while the US has 5,200.
Caretaker Iraqi Prime Minister Adel Abdul Mahdi spoke in favour of US and other foreign forces leaving the country, although most Sunni and Kurdish MPs boycotted the vote.
A UK government spokesman said that coalition forces were in Iraq to protect its people and others from the Islamic State group.
“We urge the Iraqi government to ensure the coalition is able to continue our vital work countering this shared threat,” he said.
Meanwhile, a British frigate and destroyer – HMS Montrose and HMS Defender – are to start accompanying UK-flagged ships through the Strait of Hormuz in the Gulf, where a tanker was seized by Iran last July.
In a joint statement issued late on Sunday night, Mr Johnson, Germany’s Angela Merkel and France’s Emmanuel Macron said the current cycle of violence “must be stopped” and called on Iran to refrain from further violent action and proliferation.
The three leaders said they were concerned by the “negative” role Iran has played in the region but called on “all parties to exercise utmost restraint and responsibility”.
With tensions rising in the region, Iran has responded by vowing revenge and announcing it will no longer abide by the restrictions in its 2015 nuclear deal.
The deal limited Iranian nuclear capacities in exchange for the lifting of economic sanctions.
In their statement, the three European leaders urged the country to “reverse all measures inconsistent with” the deal.
Mr Johnson said he spoke to President Trump on Sunday about the assassination of the Iranian general, who spearheaded the country’s military operations in the Middle East as head of the elite Quds Force.
The White House said the two leaders had discussed the current situation and “reaffirmed the close alliance between the two countries”.
Following warnings from Iran, Mr Trump said that the US would respond in the event of retaliation for Soleimani’s death, “perhaps in a disproportionate manner”.
He repeated a threat to target Iranian cultural sites, saying the US would “strike very fast and very hard” if Tehran attacked Americans or US assets.
In response, a No 10 spokesman said: “There are international conventions in place that prevent the destruction of cultural heritage.”
Earlier on Sunday, in his first public statement since Soleimani’s death, Mr Johnson said the 62-year-old had been “responsible for a pattern of disruptive, destabilising behaviour in the region”.
“Given the leading role he has played in actions that have led to the deaths of thousands of innocent civilians and western personnel, we will not lament his death,” Mr Johnson said.
“It is clear, however, that all calls for retaliation or reprisals will simply lead to more violence in the region and they are in no-one’s interest.”
Mr Johnson said the UK was in “close contact” with all sides to encourage de-escalation and said Parliament will be updated when it returns on Tuesday.
On Monday, former foreign secretary Jeremy Hunt told BBC Breakfast one “heartbreaking” result of the crisis was that it is now going to be “much harder” to secure the release of British-Iranian woman Nazanin Zaghari-Ratcliffe.
She is jailed in Iran over spying allegations that she denies.
Mr Hunt also said the UK and Europe needs to recognise there is a “fault line” in the Western alliance due to a “disparity in defence spending”.
“When it comes to big matters of global security we’re not putting our money where our mouth is,” he said.
Mr Trump has made repeated complaints over the defence spending of other Nato allies.
In terms of its gross domestic product (GDP, the total value of goods produced and services) the US spent roughly 3.4% on defence in 2019, according to Nato estimates, while the average in European Nato countries and Canada was 1.55%.
Meanwhile, retired army officer Sir Simon Vincent Mayall warned on Radio 4’s Today programme that British troops serving in the Middle East could “possibly” be killed in retaliation attacks on US soldiers.
The Ministry of Defence adviser said western allied troops stationed in neighbouring Iraq were “joined at the hip” and that casualties could be shared in Iraq if Iran hits back.
Foreign Secretary Dominic Raab, who told the BBC’s Andrew Marr show that he learned of the US attack on Soleimani “as it happened”, spoke to the Iraqi prime minister on Sunday morning.
Mr Raab defended the killing because of the US’s “right to self-defence” against Soleimani’s use of militia’s to destabilise the region and attack Western forces.
He also defended Mr Johnson for being on holiday as the crisis unfolded, saying that he had been “in constant contact with the prime minister over the Christmas break on a whole range of foreign policy issues”.
Shadow foreign secretary and Labour leadership candidate Emily Thornberry accused the prime minister of “sunning himself” while the chief civil servant chaired three meetings of Cobra, the government’s emergency response committee.
Shadow justice secretary Richard Burgon, who is standing to be Labour deputy leader, said Mr Johnson’s response was “pathetic”, adding that he should stand up to a US president “recklessly threatening to launch a war”.