Britons in Lebanon have been warned the UK cannot guarantee getting them out quickly if the “febrile and fragile” situation deteriorates.

Foreign Secretary David Lammy urged British nationals in the country to leave by commercial flights or on a UK-chartered plane due to depart on Wednesday, warning that the airport could be closed if the fighting continues.

Israel has begun a ground offensive in southern Lebanon, carrying out what it described as “limited, localised” operations targeting Iran-backed Hezbollah militants.

Mr Lammy urged all sides to back away from the risk of all-out war in the Middle East and demanded immediate ceasefires in both Lebanon and Gaza, where Israel is fighting Hamas.

The charter aircraft from Lebanon on Wednesday follows efforts to secure seats on the remaining commercial flights out of Beirut, including one to Heathrow on Tuesday.

The UK has already deployed troops to Cyprus in case the situation deteriorates further and an emergency evacuation is needed.

Mr Lammy told broadcasters at the Foreign Office: “I intend to put on a charter flight using commercial services tomorrow, and I’m seeking more capacity over the coming days so that people can return to our country over the next few days whilst the airport is still open.

“But I have warned and cautioned now for months that we have seen, in previous crises between Israel and Lebanon, the airport close, and we cannot guarantee that we will be able to get people out in speedy fashion.

“And of course, this is now turning into a very, very concerning situation on the ground.”

Some 4,000-6,000 British nationals are thought to be in Lebanon and they have been encouraged to register with the UK authorities as efforts are stepped up to provide routes out on flights.

British nationals and their spouses, partners and children under 18 are eligible for the UK charter flight, and those who are vulnerable will be prioritised.

The Foreign Secretary added: “We cannot make guarantees in what is a febrile and fragile situation and I suspect more people are coming forward because they recognise that in previous conflicts of this kind it has been quite hard, actually, to get out of harm’s way.”

He warned all sides to come to the table to avoid a wider war in the Middle East.

“None of us want a return to the years in which Israel found itself bogged down in a quagmire in southern Lebanon and pitched battles between Israeli soldiers and of course the Lebanese side,” Mr Lammy said.

He added: “We have been warning for months that we risk a regional war with escalation on all sides and that is why we want to see an immediate ceasefire in Gaza and an immediate ceasefire in Lebanon.

“It is politics, discussion and diplomacy that will solve the problems before us and we urge, with partners, restraint at this time.”

Lebanon Israel
Smoke rises from an attack in Beirut, Lebanon, after Israel invaded in the early hours of Tuesday (Hussein Malla/AP)

Mr Lammy has held talks with his Iranian counterpart in recent days.

Asked what message he had for Tehran, the Foreign Secretary said: “We are urging restraint.

“None of us want to see a regional war, the price would be huge for the Middle East and it would have a significant effect on the global economy.”

In a brief announcement released in the early hours of Tuesday morning by the Israel Defence Forces (IDF), the military said it was targeting Hezbollah in areas close to the border between the two nations.

The IDF added that air force and artillery units were carrying out attacks to support forces on the ground.

Rear Admiral Daniel Hagari, the Israeli military’s top spokesperson, said troops were conducting “localised ground raids” on Hezbollah positions in southern Lebanon to ensure that Israeli citizens could return to their homes in the north.

The IDF gave no details as to how long the operation in southern Lebanon would last but said its army had been training and preparing to cross the border to fight for months.