Foreign Secretary Dominic Raab said a war was in no one's interest as he described Iran's assassinated top general Qasem Soleimani as a "regional menace".

Britain is preparing to deploy the Royal Navy to escort UK-flagged commercial shipping through the Strait of Hormuz.

The US on Friday killed Soleimani in a drone strike near Baghdad international airport that raised fears of a new war in the Middle East.

"The US will take their own operational judgement call but they've got the right of self defence," Raab told Sky News television.

Raab said he spoke to Iraq's President Barham Saleh on Saturday and Prime Minister Adel Abdel Mahdi on Sunday.

"We want to see de-escalation, we're going to do everything we can to protect the UK diplomatic missions and we're going about that business," he said.

Raab said there needed to be "a route through this which allows Iran to come in from the international cold -- and that opportunity is there for them if they do the right thing".

Raab also confirmed that he has a meeting with US Secretary of State Mike Pompeo next week.

Meanwhile the Ministry of Defence said late Saturday that the frigate HMS Montrose and HMS Defender, a destroyer, "will resume accompaniments of UK-flagged commercial vessels" in the strait.

Defence Secretary Ben Wallace said: "I have instructed preparations for HMS Montrose and HMS Defender to return to accompanying duties of Red Ensign shipping. The government will take all necessary steps to protect our ships and citizens at this time."

The practice of escorting ships in the Strait of Hormuz was stood down in November, after being used during the fall-out from the seizure of the British-flagged Stena Impero tanker by Iran in July.

In a statement on Twitter, Wallace said he spoke with his US counterpart Mark Esper on Friday.

Wallace said US forces had been "repeatedly attacked by Iranian-backed militia" in Iraq during "the last few months".

"General Soleimani has been at the heart of the use of proxies to undermine neighbouring sovereign nations and target Iran's enemies," he said.

"Under international law the United States is entitled to defend itself against those posing an imminent threat to their citizens."

The British government on Saturday advised UK nationals to avoid travelling to Iraq and Iran.

Prime Minister Boris Johnson was due home from his Christmas break in the Caribbean on Sunday and Raab defended him for not returning earlier following Friday's assassination of Soleimani.