BAMAKO, Mali — In an overnight land and air assault, French forces took control of the radical Islamist haven of Gao in northern Mali, France’s defense minister said Saturday, marking the biggest gain yet of the two week-long military intervention.The speed of the attack, arriving just a week after the French and Malian forces recaptured the Islamist-held town of Diabaly in central Mali, suggested that French forces planned to also push toward to the other two extremist strongholds of Timbuktu and Kidal.Much will depend on the type of resistance they will face in the upcoming days from the al-Qaeda-linked militants and their sympathizers, who seized a vast arc of northern Mali last spring in the aftermath of a coup that destabilized Mali’s central government. Most of the jihadists appeared to have melted into the population or left Gao ahead of the offensive.Yahya Abu Al-Hamman, a top leader of Al-Qaeda in the Islamic Maghreb, the terror network’s West and North Africa wing, said the jihadists had withdrawn for tactical reasons. He promised that its fighters would resist what he described as the "new Crusader aggression” in comments published by the television network Al Jazeera on its Web site. AQIM is one of three core groups controlling northern Mali. As of Saturday night, it remained unclear exactly how much of Gao, the largest town in the north, was under the control of French and Malian forces. Some news agencies were reporting that only the airport and a strategic bridge at the entrance to the town had been captured.In a statement, French Defense Minister Jean-Yves Le Drian said that extremist fighters "saw their means of transport and their logistics sites destroyed” by the advancing forces. The French troops, he said, took control of the town and then handed it over to the Malians to secure, adding that troops from Chad and Niger were also expected to arrive in Gao soon. The mayor of Gao, Sadou Diallo, who had fled to the capital Bamako last year, also returned on Saturday, Le Drian said.Initially, French forces did come briefly under fire by the militants. "The rebels have melted in to the local population. There is harassment. The operation is still under way. It is a bit complicated,” a French officer in Mali, who asked not to be named, told Reuters. A dozen Islamist fighters were killed, according to the French military, with no deaths or injuries suffered by French troops.Residents in Gao could not be reached by phone to independently corroborate the assertions by the French defense ministry because phone networks have been down for days in the area. The offensive came a day after the jihadists blew up another bridge near the Niger border in an effort to slow down African forces preparing to enter northern Mali.Gao has been under the control of the Movement for Oneness and Jihad in West Africa, known as MUJAO, an offshoot of AQIM.Agencies