Preparations are being made to rescue UK citizens from Lebanon, the British ambassador in Beirut has said.
James Watt says there are a "number of options" open to assist Britons in the country following Israeli air strikes.
Two Royal Navy ships, aircraft carrier HMS Illustrious and assault ship HMS Bulwark, are heading to the Middle East on stand-by for a rescue operation.
British military helicopters based in Cyprus are also on their way to Beirut to support consular and embassy staff.
Other countries including Spain, Italy and Greece have already begun removing their nationals from the capital.
US security teams have arrived by helicopter at the American Embassy in Beirut, to plan the evacuation of US citizens.
Mr Watt said several Britons had already left Lebanon but the advice was to stay put.
"The situation has been very difficult since last Wednesday when the attacks began and our citizens have been advised by us and the Foreign Office to stay where they are, keep their heads down and keep in touch with us and be prepared to move if we think it's safe for them to move and with our help," he said.
"And that's what's being going on, it's still going on and there are a number of options which we can bring into play which we are preparing now but in the meantime we're asking our citizens to stay in touch with us and to remain calm and to remain where they are."
He said roads both to the east and north of Beirut had been subject to air raids - as have the airport's runways so no flights can go in or out.
Mr Watt added: "These ships will clearly give us important new options and it remains to be seen whether we get to the point of having to evacuate.
"But if we do, yes, we'll have much better options and we should be able to provide a very good level of service".
The rapid deployment team of helicopters from Cyprus is due to arrive shortly in Beirut, where it will initially offer help to the British consular and embassy staff.
It is carrying EU special representative Javier Solana.
A Foreign Office spokesman said: "There are no immediate plans to use the helicopters to evacuate, but that situation may change in the next few hours."
Susannah Graham, from Brighton, had been working in Beirut for the United Nations Relief and Works Agency (UNRWA) in a Palestinian refugee camp.
She had been living in the south-east of Beirut, near areas controlled by Hezbollah but when the attacks started fled to a Christian village in the hills north of Beirut.
She said: "I just wish those people that could exert pressure on Israel and haven't could stay here for a night and see what it's like - Tony Blair and his family."
Jolie Boyle had travelled to the Lebanese capital to work as a DJ.
She said: "The British Embassy aren't doing anything about it, and if I wait around for them, I don't know how long I'm going to be here.
"I'm on my own, it's lonely. My family's worried about me, everyone wants to know what's happening."
UK FOREIGN OFFICE ADVICE
Advice to British nationals in Lebanon is to stay put but be ready to move at any time
British and dual nationality citizens should call the Foreign Office on 0207 008 1500
Two Royal Navy ships heading to the Middle East on stand-by for rescue operation.
Britons in Israel should avoid all but essential travel areas within 25km of northern border
BBC political correspondent Mike Sargeant says it would take several days for HMS Illustrious, which is in Gibraltar, and HMS Bulwark, which is off Barcelona, to be operationally ready for an evacuation.
He added that any such measures would need the co-operation of the Israelis, and negotiations were going on at a high level.
More than 100 Spaniards have been flown to Madrid via the Syrian capital Damascus, an Italian convoy of vehicles has left Beirut for Syria, and a plane chartered by Greece brought 90 people to Athens from Damascus.
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