French troops have taken control of the airport of Mali's northeast town of Kidal, the last urban stronghold held by Islamist rebels.

The troops are wrapping up the first phase of a military operation to wrest northern Mali from rebel hands.

A three-week ground and air offensive by French forces aimed at initially ending a ten-month Islamist rebel occupation of major towns is expected to eventually hand over to a larger African force.

The Africans' task will be rooting out insurgents hiding in the desert and mountains near Algeria's border.

"They (the French) arrived late last night and deployed in four planes and some helicopters," Haminy Belco Maiga, president of Kidal's regional assembly of Kidal, told Reuters.

However, the deployment of French troops to remote Kidal puts them in direct contact with pro-autonomy Tuareg MNLA rebels operating there.

The Tuaregs, whose separatist rebellion last year was hijacked by the Islamist radicals, say they are ready to fight al-Qaeda, but many Malians blame them for triggering the collapse of democracy and division with their northern revolt.

France's military operation in its former West African colony involves around 3,500 troops on the ground backed by warplanes, helicopters and armoured vehicles.

It is aimed at heading off the risk of Mali being used as a springboard for jihadist attacks in the wider region or Europe.

French and Malian troops retook the major Saharan trading towns of Gao and Timbuktu at the weekend.

There were fears that many thousands of priceless ancient manuscripts held in Timbuktu, a UNESCO World Heritage site, might have been lost during the rebel occupation, but experts said the bulk of the texts were safe.

The United States and European governments strongly support the Mali intervention and are providing logistical and surveillance backing but do not intend to send combat troops.

The MNLA rebels, who want greater autonomy for the desert north, said they had moved fighters into Kidal after Islamists left the town earlier this week.

"For the moment, there is a coordination with the French troops," said Moussa Ag Assarid, the MNLA spokesman in Paris.

There were no reports of Malian government troops being in the town.

The MNLA took up arms against the Bamako government a year ago, seeking to carve out a new independent desert state.

After initially fighting alongside the Islamists, by June they had been forced out by their better armed and financed former allies, who include al-Qaeda North Africa's wing, AQIM, a splinter wing called MUJWA and Ansar Dine, a Malian group.

But as the French wind up the successful first phase of their offensive, doubts remain about just how quickly the UN-backed African intervention force can be fully deployed in Mali to hunt down the retreating al Qaeda-allied insurgents.