PARIS — Amid reports of continued skirmishes with Islamist extremists driven out of the main settlements of northern Mali, France renewed a promise on Wednesday that its soldiers would begin returning home within weeks, handing over authority to West African and Malian units charged with keeping the vast desert area under government control.

But French officials acknowledged that, despite their claimed military successes so far, new hostilities had erupted on Tuesday near the northern town of Gao between what were depicted as remnants of the insurgents and French and Malian forces, possibly foreshadowing a new phase in the conflict.