Britain's navy will accompany UK-flagged ships through the Strait of Hormuz to provide protection after the US killing of Iranian military commander Qassem Soleimani inflamed tensions in the region.

An EU flag is seen in front of a UK flag outside the Houses of Parliament in London, Britain, on Jan. 17, 2019. Photo:Xinhua

Britain's defense minister, Ben Wallace, ordered the HMS Montrose and HMS Defender to prepare to return to escort duties in the major oil shipping route as Prime Minister Boris Johnson came in for criticism for his silence over the killing.

Media reports have said Johnson is on holiday in the Caribbean.

"The government will take all necessary steps to protect our ships and citizens at this time," Wallace said in a statement.

Britain was forced to defend its ships through the world's most important shipping route last year after Iranian commandos seized a British-flagged tanker in the Strait.

British forces had previously captured an Iranian oil tanker near Gibraltar that was accused of violating sanctions on Syria. The killing of Soleimani has raised fears that tankers could be targeted again.

Wallace said he had spoken to his US counterpart, Defense Secretary Mark Esper, and urged restraint on all sides.

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

Jeremy Corbyn, the outgoing leader of the opposition Labour Party, said he had written to the British prime minister to ask what was being done for protection.