The prime minister has told Britons in Lebanon to “leave immediately” as around 700 UK troops are deployed to Cyprus in case an emergency evacuation is needed.

Sir Keir Starmer said “we are ramping up the contingency plans… in light of the escalation”, with fears growing of all-out war between Israel and Hezbollah.

“It is important that we be really, really clear: now is the time to leave,” the PM said.

Defence Secretary John Healey – who chaired a meeting of the UK’s emergency COBRA committee earlier – also urged all Britons to leave Lebanon “now”.

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Two British warships are already in the region and would be used if any evacuation operation is ordered. Royal Air Force planes and helicopters are also on standby.

A major UK military base in Cyprus – RAF Akrotiri – would be an important staging post.

The deployment of military personnel will happen in the coming hours. They will be supported by Border Force and Foreign Office officials.

The move marks a significant ramping up of UK efforts to prepare for a potential large-scale evacuation operation – a complex and dangerous move that has long been anticipated as a possibility given the volatility on the ground.

A government statement described it as “the first phase of its contingency plans following significant escalation between Israel and Hezbollah in recent days”.

Thousands of British nationals are in Lebanon.

Sir Keir said he was “worried about the situation” in Lebanon, adding: “I think we need to be clear we need de-escalation, we need a ceasefire, we need to pull back from the brink.”

In a sign of growing concern, Mr Healey left the Labour Party conference early to chair the COBRA meeting of ministers as well as intelligence chiefs and diplomats.

“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,” the defence secretary said in a statement afterwards.

“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.”

HMS Duncan, a Type 45 destroyer, and RFA Mounts Bay, a Royal Fleet Auxiliary ship, are already in the eastern Mediterranean ready to mobilise.

It is not the first time this year that the military has scrambled to prepare for a potential evacuation of British nationals from Lebanon.

Just last month, more than 1,000 military personnel were on standby in Cyprus and the UK to mobilise as tensions soared. That level of readiness was subsequently eased but it is now being ramped back up, with the crisis far more grave.

In the past week, Israel has launched its biggest offensive against Hezbollah – which is backed by Iran – since the two sides went to war in 2006. Hezbollah’s military wing is considered a terrorist organisation by the UK government.

The operation began with the detonation of thousands of pagers and walkie-talkies used by the group – though Israel has not confirmed it was behind this covert hybrid attack.

It quickly evolved into overt warfare, with Israeli jets launching punishing waves of airstrikes. The Israel Defence Forces said they targeted Hezbollah weapons sites and killed a number of senior commanders. However hundreds of people have been killed and thousands injured, including women and children.

Tens of thousands of people have been forced to flee their homes in southern Lebanon.

The Israeli government says the aim of its operation is to stop Hezbollah from being able to fire into northern Israel – something the militant group has done since a day after the October 7 Hamas attacks on Israel, which triggered the war in Gaza.

The Hezbollah strikes have forced tens of thousands of Israeli citizens to flee their homes in the north of Israel. The government says it wants to enable them to return home – a goal that Hassan Nasrallah, the leader of Hezbollah – has vowed to thwart.

The Israeli operation – which has dealt a punishing blow to Hezbollah – raises the possibility of Hezbollah using its arsenal of longer rage missiles to hit targets deeper inside Israeli territory – such a move would almost certainly trigger an Israeli ground attack.