A commercial flight is being chartered by the government from Lebanon to help Britons escape the escalating violence in the region.
The evacuation flight is due to leave Beirut-Rafic Hariri International airport on Wednesday.
The government said it has worked with partners in recent weeks to increase capacity on commercial flights to enable British nationals to leave, and has now chartered a flight to provide additional capacity.
Vulnerable British nationals and their spouse or partner, and children under the age of 18, will be prioritised for the flight.
But the number of seats available was not disclosed by the Foreign Office.
“Those who have registered their presence with the Foreign, Commonwealth & Development Office will be sent details on how to request a seat,” a statement said.
“British nationals should not make their way to the airport unless they have a confirmed seat on the plane.”
The move came as Israel started a ground assault against Hezbollah in southern Lebanon overnight
Britons had previously been advised to book flights out of the country – but there were limited options available, with most airlines except the national carrier MEA having cancelled flights.
The Ministry of Defence has sent nearly 700 troops to nearby Cyprus to prepare for the possible evacuation of British nationals from Lebanon and the government “continues to advise against all travel to Lebanon”.
A statement added: “The safety of British nationals in Lebanon, Israel and the Occupied Palestinian Territories (OPTs) continues to be the UK government’s utmost priority and the FCDO urges everyone to continue to follow the relevant travel advice, exercise caution, and monitor media in Lebanon for developments.”
Foreign secretary David Lammy said: “The situation in Lebanon is volatile and has potential to deteriorate quickly.
“The safety of British nationals in Lebanon continues to be our utmost priority.
“That’s why the UK government is chartering a flight to help those wanting to leave. It is vital that you leave now as further evacuation may not be guaranteed.”
The UK has been calling for a ceasefire between Lebanese Hezbollah and Israel for more than a week and that further escalation must be avoided.