KONNA, Mali — French forces took control of the Islamic rebel stronghold of Gao, the French government said Saturday, winning the biggest prize yet in the battle to retake the northern half of Mali.

Gao, which lies 600 miles northeast of the capital, Bamako, has for months been under the control of one of several Islamist groups seeking to overrun Mali. French warplanes have been pounding the city since France joined the fight at Mali’s request on Jan. 11.