French forces met no resistance in northern Mali Wednesday as they took control of Kidal, the Islamists' last major town, as the two-week-old mission scored another success in its effort to dislodge al-Qaeda-linked militants.

French and Malian troops haveĀ recaptured two of the other provincial capitals, Timbuktu and Gao, in recent days, and been welcomed by overjoyed crowds. However, already concerns are emerging about whether the Islamists will try to return once France hands over the military operation to Mali and soldiers from neighbouring countries.

"Nobody questions France's rapid deployment but the ability to hold on to the cities and territory is an immense challenge. It is not clear how they will be able to sustain the recent gains," said Alex Vines, head of the Africa program at Chatham House.

"The Islamist extremists have not been defeated; they have melted into the heat haze of the desert."

Many fear the Islamists now will attempt to hide among civilian populations in small outlying villages, only to return and attack the weaker African forces once the French are gone.

The Islamists are believed to have an elaborate system of caves and other desert hideouts that they have constructed over the last year as momentum for a West African regional military intervention stalled.

French forces take Kidal airport

Haminy Maiga, the interim president of the Kidal regional assembly, said French forces met no resistance when they arrived late Tuesday.

"The French arrived at 9:30 p.m. aboard four planes, which landed one after another. Afterwards they took the airport and then entered the town, and there was no combat," said Maiga, who had been in touch with people in the town by satellite phone as all the normal phone networks were down.

"The French are patrolling the town and two helicopters are patrolling overhead," he added.

In Paris, French army Col. Thierry Burkhard confirmed that the airport was taken overnight and described the operation in Kidal itself as "ongoing."

France's defence minister said bad weather was hampering the troops' progress out of the airport.

On Tuesday, a secular Tuareg rebel group had asserted that they were in control of Kidal and other small towns in northern Mali. Maiga said those fighters had left Kidal and were at the entry posts on the roads from Gao and Tessalit.

France, the former colonial ruler, began sending in troops, helicopters and warplanes on Jan. 11 to turn the tide after the armed Islamists began encroaching on the south, toward the capital.

French and Malian troops seized Gao during the weekend, welcomed by joyous crowds. They took Timbuktu on Monday. The Islamists gave up both cities and retreated into the surrounding desert.

To help battle the Islamists in their desert hideouts, a U.S. military official says the Pentagon is considering setting up a drone base in northwest Africa to increase intelligence collection.

While most crowds in the freed cities have been joyous, months of resentment toward the Islamists already has erupted into violence in Gao.

Video footage filmed by an amateur cameraman and obtained by The Associated Press shows a mob attacking the symbol of the oppressive regime, the Islamic police headquarters.

Some celebrate cheering "I am Malian," while others armed with sticks and machetes attack suspected members of the Islamist regime. The graphic images show the mob as they mutilate the corpses of two young suspected jihadists lying dead in the street.

France's president said his country's forces would stay in Mali as long as necessary, but the French also have said they expect troops from African nations to take the lead as soon as they are able. There are now some 2,900 African soldiers in Mali, including 1,400 from Chad who are used to fighting in harsh, desert terrain like northern Mali.

Mali's military was severely affected by last year's coup and has a reputation for disorganization and bad discipline. Already Malian soldiers have been accused of fatally shooting civilians suspected of links to the Islamists. The military has promised to investigate the allegations.