PARIS (Reuters) - Malian troops backed by French soldiers and attack helicopters killed 15 Islamists in Gao on Thursday in fighting to retake a mayor's office occupied by the militants, France's Defense Ministry said on Friday.

Four Malian and two French soldiers were wounded in the fighting that erupted after Islamists were reported to have infiltrated the town in northern Mali. Calm had returned in the afternoon, the ministry said on its website.

(Reporting By Nicholas Vinocur; Editing by Janet Lawrence)