TIMBUKTU, Mali — French troops began to withdraw from Timbuktu Thursday after securing the fabled city as they ramped up their mission in another northern Mali city, searching for extremists who may be mixing among the local population. French military spokesman Col. Thierry Burkhard said Thursday that the operation to secure Gao is still under way, nearly two weeks after French and Malian troops moved into the area. New clashes nearby raised questions about how solid a hold the French military has on the strategic area. There is a risk of "residual presence" of terrorists mixed among the population, Burkhard said from Paris. Extremists fired rocket launchers at French troops near Gao on Tuesday. UN Secretary-General Ban Ki-moon told a group of journalists Thursday that the military operation "so far has been effective and successful." "All these jihadists and armed groups and terrorist elements — seemingly — they have fled somewhere,' he said. "Our concern is that they may come back. As you have seen yesterday, they are hitting back in some areas. It is good that Timbuktu and Gao and all these major cities have been cleared." Meanwhile French troops began to draw out of Timbuktu, after greater successes in securing the desert city. Soldiers in fatigues could be seen pushing an artillery cannon onto the barge crossing the Niger River, located on the southern perimeter of Timbuktu. France has commandeered the river crossing, and on Thursday small convoys of military vehicles were lining up, waiting for the barge, including armored cars, trucks covered with camouflage-colored tarps, and vehicles loaded with supplies, like cartons of bottled water. While the population of Timbuktu is anxious, worrying that the departure of French troops will open the door for the militants to return, French military officials said they had fulfilled their mission here. "We have succeeded in handing over the majority of our responsibilities to the Malian army and now she will assume our duties. But we will not leave the city of Timbuktu completely," said Capt. Franck, an official with the French operation. He gave only his first name in keeping with military protocol. He said some French forces will stay because "once we are gone, these people will come back in order to trouble the population. At the same time, we can't stay indefinitely." "It really worries me to see the French military leave right away," said Abdel Kader Konta, the village chief of Korioume, the locality from which the troops were embarking onto the barge. "We think it's too early for them to leave because the Islamists have not fully quit the city. Some of the militants have simply shaved their beards and blended into the population. Before the French leave, they should assure themselves that security has been restored." Curious onlookers gathered near the river crossing to watch the French departure, which is expected to be phased over five days. Several had long faces, despondent with worry. Suicide bombing in north Mali A suicide bomber hit a checkpoint in northern Mali on Friday, killing only himself in the first known suicide bombing since French military forces intervened in this chaotic African nation. Malian military spokesman Modibo Traore confirmed that a suicide bomber attacked a checkpoint at the entrance to Gao around 6 a.m. on Friday. The bomber, who was wearing an explosive belt, was the only casualty. The bomber was on a motorcycle and blew himself up just before a Malian military checkpoint. Officials at a French military base in Gao declined to comment on the attack. The suicide bombing is the first known suicide bombing in Mali since the military intervention. — AP