"They've gone past Niafounke and since yesterday evening are at the gates of Timbuktu," a Malian military source said, adding that the French and Malians had not so far encountered any resistance from the rebels at Timbuktu.
The source said the advancing troops had paused outside to prepare a strategy for entering the town, a labyrinth of ancient mosques and monuments, and for flushing out any Islamist fighters.
The US and Europe are backing the UN-mandated Mali operation as a counterstrike against the threat of radical Islamist jihadists using the West African state's inhospitable Sahara desert as a launching pad for international attacks.
Following relentless French air strikes against Islamist rebel positions and vehicles, the fast-moving French-led military offensive in Mali on Saturday seized Gao, the largest town in the north, which had also been held by the rebels.
As the French and Malian troops push into northern Mali, where another major Saharan town, Kidal, also remains in rebel hands, African troops from a continental intervention force expected to number 7700 are being flown in.
Meanwile, the US is to fly tankers to refuel French jet fighters and bombers attacking militants affiliated with al Qaeda.
US Defence Secretary Leon Panetta told his French counterpart Jean-Yves Le Drian about the US decision to provide aerial refueling support. Mr Panetta has said the US has no plans to put combat troops in Mali.