ABIDJAN, Cote d'Ivoire - Heavy arms fire rang out on Wednesday near Cote d'Ivoire's presidential residence as the country's incumbent leader remained holed up in a bunker there despite mediation efforts to force his surrender.

A diplomat who spoke on condition of anonymity because of the sensitivity of the matter said the country's forces backing internationally recognized leader Alassane Ouattara were attacking the compound again where Laurent Gbagbo has hunkered down with his family.

Gbagbo representative Toussaint Alain, speaking to The Associated Press in a phone interview from Paris, said Gbagbo's residence was being bombarded by the French army, but the French military denied the claim.

"France will be held responsible for the death of President Gbagbo, his wife and family members and all those who are inside the residence, which is being bombarded by the French army," he said, adding "there is a real danger" that Gbagbo and the others could be killed in the operation.

French military spokesman Thierry Burkhard denied that French forces were firing at Gbagbo's residence, saying no French or UN operation was underway. France has helicopters patrolling Abidjan, helping guide ground forces and rescue people trapped in dangerous areas, he said.

Ouattara's forces have received strict instructions to take him unharmed, said several members of the president's cabinet.

Gbagbo refused to accept defeat in last year's election and took his country to the precipice of civil war in his bid to preserve power. His security forces are accused of using cannons, mortars and machine guns to mow down opponents in the four months since Ouattara was declared the winner of the contested vote.

But analysts say Ouattara is acutely aware that while he won last year's election with 54 percent of the vote, Gbagbo received 46 percent - representing nearly half the electorate. A diplomat who speaks to Ouattara frequently said that the leader is aware of the danger involved at this stage, because if Gbagbo is killed it may galvanize his supporters.

Choi Young-jin, the top United Nations envoy in Cote d'Ivoire said by telephone that Gbagbo's surrender was "imminent".

"He accepted (the) principle of accepting the results of the election, so he doesn't have many cards in his hands," Choi said. "The key element they are negotiating is where Mr Gbagbo would go."

French Foreign Minister Alain Juppe has said that Gbagbo would be required to relinquish power in writing and must formally recognize Ouattara, the internationally backed winner of the November election.

After amassing at the outskirts of the city on Monday, forces loyal to Ouattara seized the presidential residence where Gbagbo has been holed up overnight. They moved in after the United Nations agreed to act on a Security Council resolution giving their peacekeepers the right to take out Gbagbo's heavy artillery.

Mi-24 helicopters aided by French troops bombarded the outer perimeter of the compound. Those living nearby said the earth shook with each blast.

US President Barack Obama said on Tuesday the role of the United Nations was necessary to end the conflict. Ouattara's forces had taken over three-quarters of the countryside between Monday and Wednesday of last week, but then faltered when they reached Abidjan, where Gbagbo had created a protective radius, manned by his most faithful soldiers.

AP