Royal Navy warships have been ordered to escort British-flagged vessels in the Persian Gulf, in the wake of the US killing of Iran’s top military leader.
It comes amid fears Iran will seek revenge for the assassination of Qasem Soleimani in a US drone strike in Iraq.
Foreign Secretary Dominic Raab said Gen Soleimani was a “regional menace” and the UK aims to “stabilise” the crisis.
Boris Johnson is due to return to the UK after a 12-day holiday and will talk to foreign leaders in the coming days.
Gen Soleimani was killed this week in a US drone strike in Baghdad, Iraq.
The killing of Gen Soleimani marks a major escalation in tensions between the US and Iran, with Tehran vowing to avenge his killing.
US President Donald Trump last night tweeted that the US will strike 52 Iranian sites “very fast and very hard” if Tehran follows through with its vow of revenge.
Speaking to Sky’s Sophy Ridge programme, Mr Raab, who will travel to Washington this week to meet US counterpart Mike Pompeo, said the UK was working with “our European and American friends” to try and “de-escalate and stabilise the situation”.
He added: “We also need to be clear there is a route through which allows Iran to come in from out of the international cold.”
Mr Raab said he had already spoken with Iraq’s president and prime minister, and will “reach out” to Iran’s foreign minister.
Asked whether the US was right to order the killing of Gen Soleimani, Mr Raab said the UK understands the position the US was in, adding: “The US will take their own operational judgement call. They have got the right of self-defence.”
Defence Secretary Ben Wallace said it would help protect ships and citizens amid fears Iran will seek revenge for the assassination of Qasem Soleimani.
Mr Wallace said HMS Montrose and HMS Defender will accompany UK-flagged ships through the Strait of Hormuz, as they did between July and November following the seizure of a British-flagged tanker by Iran.
He said he had spoken to his US counterpart, Mark Esper, on Friday and urged all parties to de-escalate the situation.
But Mr Wallace added: “Under international law the United States is entitled to defend itself against those posing an imminent threat to its citizens.”
Mr Johnson is expected to return to the UK later after spending almost two weeks on the Caribbean island of Mustique.
He has yet to speak publicly about the US airstrike or subsequent threats from Iran.
Outgoing Labour leader Jeremy Corbyn renewed his criticism of the PM for not cutting short his holiday and called for an urgent meeting of the Privy Council – the group that advises the Queen – over the airstrike.
Mr Pompeo had criticised America’s European allies for not being “helpful” in the wake of the assassination. However, he later said in a tweet that he was “thankful that our allies recognise the continuing aggressive threats posed by the Iranian Quds Force”.
Mr Raab is expected to meet his French and German counterparts before travelling to the US capital on Thursday.
Following the strike, the Foreign Office has hardened its travel advice for Britons in Iraq and Iran. Officials also urged those travelling to the United Arab Emirates, Turkey and Israel to “remain vigilant”.
In its advice, published on Saturday, the Foreign Office said there is a risk that British or British-Iranian dual nationals “could be arbitrarily detained or arrested in Iran”.
“The criminal justice process followed in such cases falls below international standards,” it said.
The Foreign Office also said alerts for other parts of the Middle East were being increased, with calls for citizens to “remain vigilant” in nations including Afghanistan, Israel, Lebanon, Saudi Arabia and the United Arab Emirates.
It advised people to keep up to date with developments via the media and its own travel advice.
It comes as the US has pledged to send 3,000 extra troops as a precaution. The UK has 400 troops based in the Middle East and works alongside US forces in the region.
On Saturday, around 150 people gathered outside Downing Street for an “emergency” protest organised by the Stop the War Coalition, urging the US to avoid more conflict with Iran.