(Adds deathtoll, report of hostage killing)
By Cheick Diouara
GAO, Mali, March 24 (Reuters) - Six people were killed on Sunday in a second day of fighting between Islamist rebels and Malian and French forces in the northern Malian town of Gao, authorities said.
The rebels attacked the north's largest town just days after French President Francois Hollande said Mali's sovereignty had almost been restored.
It was the third major offensive there by Islamists since the town was retaken by a French-led military operation in late January.
Mali's defence ministry said in a statement that at least four militants were killed, as well as one Malian army soldier and a civilian adolescent. It said the fighting was over by midday on Sunday.
France has deployed some 4,000 troops to Mali, alongside a regional African force, in a nine-week operation that has driven Islamists into desert hideaways and mountains near the Algerian border.
Gao is a former stronghold of the MUJWA Islamist group which controlled the town for around 10 months, imposing a violent form of sharia, Islamic law.
Intense shooting had been reported for around two hours on Saturday evening after a group of around 10 Islamists slipped past military checkpoints to enter the town. Calm returned during the night but the combat resumed early on Sunday morning, residents said.
A Reuters witness had earlier seen four Islamist fighters - two carrying Kalashnikov assault rifles, one a rocket-propelled grenade launcher and another wearing what appeared to be an explosive belt - running across a dusty street as fighting continued elsewhere in the town.
Separately, Mauritania's ANI news agency reported Al Qaeda's North African wing AQIM said it had killed a French hostage captured in northern Mali two years ago and that its other French captives were at risk because of France's intervention.
ANI reported earlier this week that an AQIM member said its fighters beheaded Philippe Verdon, who was seized in northern Mali in November 2011, on March 10.
(Additional reporting by Adama Diarra and Tiemoko Diallo in Bamako; Writing by Daniel Flynn; Editing by Jason Webb)