Al Qaeda-linked Islamist militants seized control of the headquarters of the local separatist rebels in the north Mali town of Gao on Wednesday after a bloody battle that killed at least 20, residents said.The battle follows weeks of tension between the separatist Tuareg-led MNLA and better-armed local Islamists who helped it take control of the northern two-thirds of Mali in April but whose goal is to impose sharia Islamic law across the country. "The Islamists are now controlling the situation because they are the only ones driving around in the town, some in their vehicles and others on vehicles they have recovered from the MNLA,” Gao resident Moktar Toure told Reuters by telephone."But we live in fear of an MNLA counter-offensive against the Islamists even though they are trying to reassure people that it is over,” Toure said.A spokesman of the Islamist Ansar Dine group said their militants had taken control of the governor’s residence and chased away MNLA fighters.One witness told Reuters earlier on Wednesday that the former governor’s residence in Gao which the MNLA had turned into the "palace” of the northern territory it calls the independent state of Azawad, had been heavily damaged by heavy arms fire during the battle.The fighting will add to fears of Mali becoming a potential launchpad for jihadi action. The U.N. Security Council has said it would be ready to support military intervention by Mali’s neighbours but first needs more details of their plans.