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 Islamic 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.

France launched a military operation in Mali on Jan. 11 to help the Malian government restore control. Islamic extremists linked to al-Qaida had imposed severe rule in northern Mali then started pushing toward the capital last month.

In a sign of heightened security, authorities briefly detained three Tuareg men in Gao on Thursday who were stopped after they did not have their identity papers. The men, who came from a nearby village, were in Gao because they had missed their bus to a nearby market. The mayor intervened and the men were released.

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 Islamists 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 codenamed Serval, after a sub-Saharan wildcat. 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."

French president Francois Hollande has said France could begin withdrawing its 4,000 troops from Mali as early as March. Foreign Minister Laurent Fabius reiterated that stance Thursday, saying the administration was sticking to its schedule and emphasizing the need for political as well as military action.

"Our objective cannot be achieved with arms only," Fabius said in an interview on French television BFM.

Fabius said France had carefully studied foreign interventions elsewhere in the world before undertaking the Mali mission. "It's not Afghanistan, it's not Somalia, but there are nonetheless lessons to be learned."

Still for residents of this desert capital of Timbuktu, which was subjected to 10 months of often-brutal Shariah rule, the departure of the troops is premature.

"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 Islamists 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.

"People think that the Islamists have left. But we think they are still here," said fisherman Baba Ali Sampana, who had stopped to watch their departure, standing next to his fishing canoe. "The French military should not leave right now."

Further north in the area of Kidal French Mirage 2000 and Rafale fighter jets had been hammering targets including the Islamic extremists' logistical depots and training camps. Burkhard said fighters flew around 30 sorties during the night of Feb. 2-3, striking 20 targets.

French troops are in control of the Kidal airport, while the city and surroundings are patrolled by some of the 1,800 Chadian troops taking part in the operation.

On Wednesday, France asked the Security Council to consider establishing a U.N. peacekeeping operation in Mali. France's U.N. Ambassador Gerard Araud told reporters that he started discussions on the issue during closed council consultations on Mali, but insisted that a U.N. force would deploy only when security conditions permit.

In December, the council resolution had authorized an African-led force known as AFISMA to support Malian authorities in recovering the north - an area the size of Texas - but had set no timeline for military action. The unexpected move by the al-Qaida-linked extremists pushing southward, and France's intervention, are forcing the Security Council to revamp its plan.