Mustafa Abdul Jalil, who leads the National Transitional Council (NTC), said the ultimatum applied to loyalists of Col Muammar Gaddafi in his hometown of Sirte and in other towns.

The announcement came after Col Gaddafi's wife and three of his adult children fled to neighbouring Algeria. Algeria has defended the move, which the NTC called an "act of aggression".

The anti-Gaddafi forces are trying to overcome pockets of resistance by loyalists, and preparing to advance on Sirte.

Speaking at a news conference in Benghazi, Mr Jalil said that if there was no “peaceful indication” by September 3 that Gaddafi-loyalists intended to surrender, “we will decide this manner militarily”.

The anti-Gaddafi forces made an attempt to reach Sirte last week but were fought back by loyalist troops. On Monday, fighters coming from Benghazi in the east captured the small town of Nofilia, on the road to Sirte.