In this screen grab image issued by the Prime Minister's Press Office, showing Prime Minister Boris Johnson during his New Year's message to be broadcast Tuesday Dec. 31, 2019. Johnson has said Britain can look forward to a decade of "prosperity and opportunity", as it finally ends the "rancour and uncertainty" of Brexit. (Photo: AP)

Britain’s Prime Minister Boris Johnson is due to return Sunday to the U.K., where he faces criticism for not cutting short his holiday to deal with soaring Mideast tensions.

Johnson, who celebrated the New Year on the Caribbean private island of Mustique after leading his Conservative Party to a strong majority in the Dec. 12 election, has been silent over the U.S. slaying Friday of Iranian Gen. Qassem Soleimani in a drone strike.

Soleimani’s death stoked fears that heightened world tensions could spiral into war after Iran threatened revenge against the U.S, which has sent 3,000 more soldiers to Kuwait.

British Foreign Secretary Dominic Raab has defended Johnson, saying the two have been in constant contact during this time.

The British government has upgraded its travel warning for the Middle East and dispatched two warships to escort U.K.-flagged ships passing through the Strait of Hormuz, a key shipment corridor for world oil supplies.

Jeremy Corbyn, the outgoing leader of the opposition Labour party, said Johnson “should have immediately cut short his holiday to deal with an issue that could have grave consequences for the U.K. and the world.”

In an op-ed in The Observer, Labour’s foreign policy spokeswoman Emily Thornberry, who is in the race to take over from Corbyn, said she was astonished Johnson hadn’t said anything 48 hours after the strike and wondered if he was afraid of angering U.S. President Donald Trump, who ordered the slaying.

Ed Davey, the leader of a smaller party, the Liberal Democrats, tweeted that Johnson’s silence was “deafening.”

Raab, appearing Sunday morning on British news shows, dismissed the criticism, telling Sky News that “the whole government is working closely together. We’re very clear on strategy.”

“Johnson has been in charge from the outset,” he told the BBC. “In fact, I’ve been in constant contact with the PM over the Christmas break on a whole range of foreign policy issues.”

Later this month, Johnson aims to fulfil his major campaign promise and “get Brexit done,” taking Britain out of the European Union as scheduled on Jan. 31. The U.K. then embarks on intense negotiations to hash out a trade deal with the EU, Britain’s top trading partner.

The Labour Party, meanwhile, is casting about for a new leader a fter the worst showing since 1935 in December’s general election. A raft of contenders are vying take over, with five candidates so far declaring their intention to run, including Labour’s Brexit spokesman Keir Starmer, who’s seen as the frontrunner, high-profile lawmaker Jess Philips and Thornberry.

The party’s executive committee will meet Monday to set the timetable for the leadership contest, which is expected to formally open Tuesday. The new leader is expected to be in place by the end of March.