GAO, Mali - French and Malian troops retook control of Timbuktu, a UNESCO World Heritage site, on Monday after Islamist rebel occupiers fled the ancient Sahara trading town and torched several buildings, including a library holding priceless manuscripts.

The United States and the European Union are backing a French-led intervention in Mali against al Qaida-allied militants they fear could use the West African state's desert north as a springboard for international attacks.

The recovery of Timbuktu followed the swift capture by French and Malian forces at the weekend of Gao, another major town in Mali's north that had been occupied by the alliance of jihadist groups since last year.

The two-week-old mission by France in its former Sahel colony, at the request of Mali's government, has driven the Islamist rebels northwards out of towns into the desert and mountains.

Without a shot being fired, 1,000 French soldiers and paratroopers and 200 Malian troops seized Timbuktu airport and surrounded the town on the banks of the Niger River, looking to block the escape of insurgents.

In both Timbuktu and Gao, cheering crowds turned out to welcome the French and Malian troops.

A third town in Mali's vast desert north, Kidal, had remained in Islamist militant hands. But Malian Tuareg MNLA rebels, who are seeking autonomy for their northern region, said on Monday they had taken charge in Kidal after Islamist fighters abandoned it.

A diplomat in Bamako confirmed the MNLA takeover of Kidal.

A French military spokesman said the assault forces at Timbuktu were avoiding any fighting inside the city to protect the cultural treasures, mosques and religious shrines in what is considered a seat of Islamic learning.

But Timbuktu Mayor Ousmane Halle told Reuters departing Islamist gunmen had four days earlier set fire to the town's new Ahmed Baba Institute, which contained thousands of manuscripts.

UNESCO spokesman Roni Amelan said the Paris-based UN cultural agency was "horrified" by the news of the fire, but was awaiting a full assessment of the damage.

Ali Baba, a worker at the Ahmed Baba Institute, told Sky News in Timbuktu more than 3,000 manuscripts had been destroyed. "They are bandits. They have burned some manuscripts and also stole a lot of manuscripts which they took with them," he said.

Marie Rodet, an African history lecturer at Britain's School of Oriental and African Studies, said Timbuktu held one of the greatest libraries of Islamic manuscripts in the world.

"It's pure retaliation. They (the Islamist militant rebels) knew they were losing the battle and they hit where it really hurts," Rodet told Reuters. "These people are not interested in any intellectual debate. They are anti-intellectual."