Tony Blair is to delay his annual summer holiday to continue working on a UN Security Council resolution for a Lebanon ceasefire.
Tony Blair believes the next couple of days are crucial
He is now expected to depart for his three-week break - handing power to his deputy John Prescott - in a few days.
The prime minister had previously insisted he would remain involved in solving the crisis by telephone.
Mr Blair believed the next few days would be "critical" in achieving a peace deal, Downing Street said.
Sources said the prime minister would have had secure communications at his Caribbean holiday destination, but he did not want to be on a long-haul flight and out of contact in the final stages of negotiations.
The decision is likely to be welcomed by critics in his own party who say he has not done enough to try to end the fighting in Lebanon and Israel.
France and America have been working intensively on the text of a UN resolution, which could be coupled with a second resolution authorising an international force, which France could lead.
Officials said Mr Blair spoke to UN Secretary General Kofi Annan on Thursday evening and to French president Jacques Chirac on Friday morning.
He is expected to continue working from Downing Street on Friday and wants to remain in close contact with Foreign Secretary Margaret Beckett, who has already cancelled her own holiday plans.
A Downing Street spokesman said: "The prime minister has delayed leaving for his holiday so that he can do further work trying to achieve a UN resolution and wider efforts to achieve sustained peace in the region.
"He believes the next couple of days are crucial and will be continuing his intensive diplomacy with world leaders from Downing Street."
On Thursday, Mr Blair said reports of a rift with Mrs Beckett over his Middle East policy were "complete rubbish".
He insisted his refusal - along with US President George W Bush - to join calls for an immediate ceasefire did not mean he was "indifferent" to the plight of the Lebanese people.
Such statements achieved little unless they were backed by action, he said, holding out the prospect of a UN resolution on a ceasefire "within days".
It would aim to bring about an immediate ceasefire, to be followed by the deployment of an international peacekeeping force, he told his monthly news conference in Downing Street.
Labour MP John McDonnell, who has announced he will run for the party's leadership once Mr Blair stands down, called for a recall of Parliament in order for the prime minister to be held to account for his "unforgivable" decision not to back demands for an immediate ceasefire.
The Hayes and Harlington MP will be among speakers at an anti-war rally in London on Saturday.