French-led forces today seized Mali's fabled desert city of Timbuktu in a lightning advance north as Islamists fleeing the city torched a building housing priceless ancient manuscripts.

The caravan town on the edge of the Sahara desert was the top prize in the 18-day French offensive that has stopped the Islamists' march south towards the capital Bamako and driven them from their bastions.

Only one Islamist stronghold, the town of Kidal further north, remains to be retaken.

"The Malian army and the French army are in complete control of the town of Timbuktu. Everything is under control," a colonel in the Malian army said on condition of anonymity.

Timbuktu Mayor Halley Ousmane, who is in Bamako, confirmed the town had "fallen into the hands of the French and Malians".

With another victory scored in the northern Mali juggernaut, French President Francois Hollande exclaimed: "We are winning in Mali."

However, fears soared for the city's cultural heritage when a building housing tens of thousands of manuscripts from the ancient Muslim world and Greece was set aflame.

The once cosmopolitan town and a centre of Islamic learning for centuries, Timbuktu became a dusty outpost for the extremists, who forced women to wear veils, whipped and stoned those who violated their version of strict Islamic law, and destroyed ancient Muslim shrines they considered "idolatrous".