More heavy fighting is being reported in Ivory Coast's main city of Abijan.
Forces loyal to the internationally recognised president Alassane Ouattara are reported to be closing in on the incumbent Laurent Gbagbo.
Mr Gbagbo has refused to cede power despite United Nations-approved results saying that Mr Ouattara won an election in November last year.
The BBC reports the fighting inside Abijan has reached a new level of ferocity.
Sustained heavy gunfire has been heard overnight on Monday in the city centre, around the television station and the residence of Mr Gbagbo.
A spokesperson for Mr Ouattara's government claims the residence has been overrun, but the BBC reports it is not clear what has happened to Mr Gbagbo.
The battle for Abijan is entering its sixth day, with millions of civilians still trapped by the fighting. The general leading the assault has insisted that the city will fall on Tuesday.
On Monday, UN and French helicopters fired on military camps operated by Mr Gbagbo to try to halt attacks on civilians.
Gunfire rang out across Abidjan and explosions and firing could be heard from the direction of the presidential palace.
A UN official told the BBC the operation was aimed at preventing use of heavy weapons at the military camp, which have been deployed against UN personnel and Ivory Coast civilians in recent days.
A French armed forces spokesperson says French helicopters opened fire on the military camp in support of UN peacekeepers.
Meanwhile, Mr Ouattara's ambassador in Paris says Mr Gbagbo is negotiating his surrender - a claim denied by Mr Gbagbo's adviser i France.