Keir Starmer has warned Britons in Lebanon to “leave immediately” amid escalating violence in the Middle Eastern country.
In total, 700 UK troops have been scrambled to nearby Cyprus in case an emergency evacuation is necessary.
The Prime Minister said the UK is “ramping up the contingency plans… in light of the escalation.”
He was unequivocal in his advice to any Britons still in the country, which has been bombarded by Israeli airstrikes since Monday.
Sir Keir warned: “It is important that we be really, really clear: now is the time to leave.”
Defence Secretary John Healey chaired a meeting of the UK’s emergency COBRA committee earlier on Tuesday. He likewise called on all Britons to leave Lebanon “now”.
Royal Air Force planes and helicopters are on standby in case they are needed to assist in the evacuation effort.
Meanwhile, two British warships, already in the region, would also be utilised.
In addition, the UK troops on hand are stationed at RAF Akrotiri, Cyprus.
It is unclear how many Brits are living in Lebanon, but most estimates place the figure in the tens of thousands.
The Defence Secretary left the Labour Party conference early to chair the emergency COBRA meeting.
In a statement following the meeting, he said: “Events in the past hours and days have demonstrated how volatile this situation is, which is why our message is clear, British nationals should leave now.
“We continue to urge all sides to step back from conflict to prevent further tragic loss of life. Our government is ensuring all preparations are in place to support British nationals should the situation deteriorate.
“I want to thank the British personnel who are deploying in the region for their commitment and professionalism.”