Al-Qaeda-linked fighters in Mali have bulldozed the tombs of three local Sufi saints near the desert city of Timbuktu, residents said, the latest in a series of attacks in the north that critics say threaten its cultural heritage.

Residents on Thursday said the rebels were from Ansar Dine, one of a mixture of groups now in control of northern the country.

"They arrived aboard six or seven vehicles, heavily armed," said Garba Maiga, a resident of Timbuktu, listed by UNESCO as a World Heritage Site for its ancient shrines.

"They flattened everything with a bulldozer and pulled up the skeletal remains."

The destruction of the tombs follows an attack on another shrine outside Timbuktu at the end of September and several others in July.

Residents said the tombs destroyed included those of local saints Cheick Nouh, Cheick Ousmane el Kabir, and Cheick Mohamed Foulani Macina, several kilometres outside of the city gates.

A spokesman for Ansar Dine was not available to comment.

Power vacuum

The fighters say they are defending the purity of their faith against idol worship, though historians say their campaign of destruction is pulverising a valuable part of the history of Islam in Africa.

Sufi Islam, which reveres saints and sages with shrines, is popular across much of northern Mali.

Mali descended into chaos in March when soldiers toppled the president, leaving a power vacuum that led to armed groups, some allied al-Qaeda, seizing the northern two-thirds of the country.

The UN Security Council last week passed a resolution urging African regional groups and the United Nations to present a specific plan within 45 days for military intervention in Mali to help government troops reclaim the north.

But diplomats say the challenges of putting together an African force make it unlikely an operation could be mounted before March at the earliest.