GAO, Mali – Black-robed Islamic extremists armed with AK-47 automatic rifles invaded Gao in wooden boats Sunday to launch a surprise attack on the most populous city in northern Mali, two weeks after French and Malian troops ousted the jihadists.

Gunfire echoed for hours across the city of mud-walled buildings. The combat started at about 2 p.m. in downtown Gao and the fighting was continuing as night fell. Later the sound of gunfire was replaced by the clattering of French military helicopters overhead.

The attack in Gao shows the Islamic fighters, many of them well-armed and with combat experience, are determined and daring and it foreshadows a protracted campaign by France and other nations to restore government control in this vast Saharan nation in northwest Africa.