ABIDJAN - Forces loyal to Ivory Coast's presidential claimant Alassane Ouattara launched a major assault on the presidential palace on Tuesday, driving home their campaign to oust Laurent Gbagbo after UN and French helicopters left his military bases in flames.Sustained machinegun and heavy weapons fire rang out into the morning from the direction of the palace in the commercial capital Abidjan, in the heaviest fighting since soldiers backing Ouattara entered the city five days ago.Gunfire and explosions were also heard near Gbagbo's official residence in the leafy neighborhood of Cocody early on Tuesday, as well as in Adjame, where one of Gbagbo's largest military bases is located, witnesses said."We spent the whole night locked in our house, on the floor with our hands covering our ears to block the sounds of the explosions," Jacques Djoble, a resident of Cocody, told Reuters by telephone.The United Nations peacekeeping force in Ivory Coast, supported by the French military, targeted Gbagbo's heavy weapons capabilities with attack helicopters after civilians were killed in shelling in recent days.Attacks centred on military bases in the city, but also on rocket launchers "very close" to Gbagbo's Cocody residence, UN peacekeeping chief Alain Le Roy told reporters during a news briefing late on Monday.A spokesman for Ouattara's government said late on Monday that his troops -- which have been in the city since last Thursday -- had since taken control of Gbagbo's residence. A pro-Gbagbo military source denied the claim."Despite the bombardments, we are holding all of our positions, meaning the palace, the residence and all of our military bases," the source told Reuters on Tuesday, asking not to be named.Ouattara's envoy to Paris said on Tuesday that he believed Gbagbo was in the process of negotiating his surrender, but a Gbagbo adviser also in Paris denied it, saying Gbagbo remained in his residence and would not budge.The fighting in the West African cocoa grower nation pushed cocoa prices lower on Tuesday as dealers bet on a swift end to Gbagbo's rule and a resumption of exports. The country's defaulted $2.3 billion Eurobond rose as the assault raised expectations for repayment.