by Fran Blandy

ABIDJAN (AFP) – Ivory Coast's Laurent Gbagbo was cornered and facing an end to 10 years in power Tuesday as forces for widely recognised president Alassane Ouattara pursued a military offensive to unseat him.

After doggedly refusing to accept he lost November elections, Gbagbo was reportedly negotiating his exit under fire from fighters for Ouattara who said they had launched their "final assault" after diplomacy had failed.

Heavy weapons fire shook the main city Abidjan on the second day of the all-out offensive with Gbagbo strongholds surrounded and a fight under way for control of the city's gendarmerie camp in Cocody district, residents said.

There was fierce fighting through the night, with UN and French helicopters striking Gbagbo bases late Monday, including military barracks and the presidency, to take out heavy weapons.

"I believe Laurent Gbagbo is alive," the Ouattara-appointed ambassador to France, Ally Coulibaly, said on French radio RFI.

"I have learned that he is negotiating his surrender," he said.

"What I have learned is that since yesterday he (Gbagbo) has been seeking to negotiate. It is not too late," said the diplomat, who is a close advisor to Ouattara, adding though that Abidjan had become "a rumour mill".

Coulibaly said he did not know through what channels Gbagbo was negotiating or whether a mediator was involved.

Weary of failed diplomatic efforts to resolve the post-election crisis, Ouattara's army launched a lightning offensive further north a week ago, seizing much of the country and entering Abidjan late last week.

They came up against fierce resistance after initially estimating the final showdown with Gbagbo would end within hours, but issued another ultimatum late Monday.

"The final assault for the total capture of the residence and the palace will take place in the coming hours," said Sidiki Konate, the spokesman for Ouattara's prime minister Guillaume Soro.

"The operation is expected to finish tonight," he said.

Hours earlier French and UN helicopters fired at the presidential palace, presidential residence and two military barracks held by the 65-year-old Gbagbo.

UN Secretary General Ban Ki-moon said the aim was to stop heavy weapons being used against civilians and not a declaration of war against Gbagbo.

But one of his advisers in Paris, Toussaint Alain, described the strikes as "illegal" and amounted to an "assassination attempt" on the man who took power in 2000 and postponed polls due in 2005 before allowing them to go ahead last year.

Ban accused Gbagbo's forces of having "intensified and escalated" the use of mortars, rocket-propelled grenades and heavy machine-guns against civilians.

They had also targeted the UN headquarters in Abidjan "with heavy-calibre sniper fire as well as mortars and rocket-propelled grenades". Four peacekeepers have been wounded, he said.

A UN Security Council resolution 1975 adopted on March 30 ordered sanctions against Gbagbo to push him to leave and also said the UN force should protect civilians and prevent use of heavy weapons.

While US President Barack Obama urged Gbagbo "to end his claim to the presidency", European Union President Herman Van Rompuy welcomed UN efforts to "protect the civilian population in line with the mandate given by the UN Security Council".

The French military said its action "aimed to neutralise heavy weapons positions in barracks and armoured military vehicles equipped with cannons and rocket launchers".

About 1,900 foreigners are under French military protection in Abidjan and 447 others have already left Ivory Coast, according to the French military which has taken control of the Abidjan airport.

Reports have meanwhile emerged of human rights abuses over the past week, as pro-Ouattara forces swept southwards to Abidjan, including the massacre of hundreds of civilians in the western town of Duekoue.

Months of fighting has also seen up to a million people flee their homes in Abidjan and elsewhere, many of the them into neighbouring countries, UN agencies have said, warning of a humanitarian disaster.