Britain on Sunday night withdrew families of embassy workers in Beirut over fears of war between Lebanon and Israel.

The Foreign, Commonwealth and Development Office said it was “deeply concerned with the highly volatile security situation”, adding that additional military personnel had been deployed to the region.

David Lammy, the Foreign Secretary, reiterated his advice to all British nationals in Lebanon to “leave now” while they can.

Saudi Arabia joined France, Canada and Jordan in calling on their citizens to leave Lebanon.

“In a highly volatile security context”, French nationals were “urgently asked” to avoid travelling to Lebanon, and those already in the country should leave “as soon as possible”, the foreign ministry in Paris said.

France also urged its nationals living in Iran to “temporarily leave”.

Israel is bracing for a major attack in retaliation for a double assassination in Beirut and Tehran over the last week.

World leaders have been urging both sides to step back or risk triggering a full-scale regional war.

But Israel warned it would go on the attack if struck by Iran or its ally Hezbollah in Lebanon.

Yoav Gallant, Israel’s defence minister, said: “We are ready to move quickly to attack or to respond. We will exact a price, as we have been doing in recent days from the enemy. If it dares to attack us, it will pay a heavy price.”

He was backed by Benjamin Netanyahu, the Israeli prime minister, who told his security cabinet: “I reiterate and tell our enemies: We will respond and we will exact a heavy price for any act of aggression against us, from whatever quarter.”

The US said it was sending an aircraft carrier and warplanes to the region for “every possibility”. The FCDO said the UK had sent “additional consular officials, Border Force and UK military personnel to the region”, but did not provide further details.

Tensions have increased following the assassination on Wednesday of Ismail Haniyeh, a top Hamas leader in Tehran, one day after an Israeli strike in the Lebanese capital Beirut killed Fuad Shukr, a senior military commander from Lebanese terror group Hezbollah. Both groups are backed by Iran.

Israel and the US are braced for an attack similar to that seen in April when Iran launched its first ever direct assault on Israel, with hundreds of drones, missiles and rockets. Israel retaliated at the time with a single missile strike on an air defence unit in Iran and the tit-for-tat exchanges ended after that.

Observers have questioned whether both sides are prepared to de-escalate this time around.

On Saturday night more than 30 projectiles were fired at Israel by Hezbollah without penetrating the Iron Dome air defence umbrella. Meanwhile, five rockets were launched by Hamas in Gaza on Sunday to southern Israel with one falling into Hof Ashkelon.

Two people were killed and another two seriously injured when a man from the West Bank went on a stabbing rampage in Holon, central Israel, on Sunday, heightening tensions further.

“We are doing everything possible to make sure that this situation does not boil over,” Jon Finer, the White House deputy national security adviser, said on Sunday.

At least 100,000 Israeli citizens are also believed to be stranded abroad, leading Israel’s ministry of transport to launch emergency maritime fleets to bring them home.

Over 18 airlines have cancelled flights, including British Airways.