The Liberian President, Charles Taylor, has agreed to step down on 11 August - a few days later than expected.
Control of the strategic Old Bridge in central Monrovia changes daily
The announcement came after West African ministers met Mr Taylor to discuss plans for him to go into exile in Nigeria.
The BBC's Paul Welsh says Mr Taylor is backtracking from his promise to leave the country three days after peacekeepers arrive.
A first contingent of 1,500 Nigerian troops is due to be airlifted into the capital, Monrovia, on Monday.
On Friday, the United Nations approved a multinational force to keep order after Mr Taylor steps down.
The UN Security Council authorised the deployment of a West African force to help implement a ceasefire, and its replacement by a UN peacekeeping force by 1 October.
Two American warships are nearing the Liberian coast carrying marines, helicopters and landing craft.
The warships will take up positions off the coast, but the American-drafted UN resolution makes no mention of any participation by US troops.
The transfer of power will come in a joint session of Liberia's congress, Mr Taylor told reporters.
"At 1159 on Monday (August 11) I will step down and the new guy will be sworn in," Mr Taylor said, confirming an earlier statement by Ghana's foreign minister.
But he refused to say when he would leave the country.
"The most important thing is, everything that we have said about resigning and leaving will happen," he said.
Even as Saturday's talks began, heavy fighting broke out on the outskirts of the capital, with unconfirmed reports that government forces fought their way across two key bridges leading to the commercial area of the capital.
The government forces are trying to recapture the port, which is held by the main rebel group Lurd (Liberians United for Reconciliation and Democracy).
Hundreds of civilians have been killed since fighting reached Monrovia in June, as rebel groups made gains after three years of civil war.
Lurd and a smaller rebel group Model (Movement for Democracy in Liberia) between them control at least two thirds of the country.
A day's wait
The West African envoys, from the regional grouping Ecowas, had been due to see Mr Taylor on Friday, but the meeting failed to materialise.
Mr Taylor said he was leading the fight for the second city, Buchanan, but Monrovia is full of rumours that he spent the day in his home, determined not to meet the envoys, our correspondent reports from the Liberian capital.
Mr Taylor, who has been indicted by a UN-backed war crimes tribunal in Sierra Leone, has said he will take up an offer of asylum from Nigeria - but only after peacekeepers arrive to prevent possible ensuing chaos.