The battle follows weeks of tension between the separatist Tuareg-led group MNLA and well-armed local Islamists who helped it seize the northern two-thirds of Mali in April but whose goal is to impose Sharia law across the country.
One witness said 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, was heavily damaged during the battle.
The fighting will add to fears of Mali becoming a potential launchpad for jihadi action.
The UN Security Council has said it would be ready to support military intervention by Mali’s neighbours but first needs more details of their plans.
“The MNLA and MUJWA [Movement for Unity and Jihad in West Africa] are launching rockets at each other between the two markets of the town and the governor’s building,” Gao resident Sila Askou said by telephone from the governor’s premises in which the MNLA has set up headquarters.
Gao resident Habsatou Cisse said she saw five bodies from the house in which she was sheltering. Others reported 11 and four bodies in two separate locations. They said civilians were among those killed but had no other details.
Separately, residents in the northern town of Timbuktu, 200 miles west, said they had seen armed convoys of the Ansar Dine Islamist group – a MUJWA ally – racing to Gao.
“We are going to obliterate the MNLA,” said Islamist Ousmane Toure. “Enough is enough.”