Islamist militants, swinging pick-axes and shouting God's praise, destroyed ancient tombs of Muslim saints in Mali's fabled city of Timbuktu on Saturday, sparking international condemnation.

The rampage of destruction in the UNESCO designated world-heritage city comes after three months of unrest in Mali's remote desert north which has raised fears of a new Islamist extremist haven in west Africa.

Ansar Dine and other Al-Qaeda-linked militant groups have imposed strict sharia law since sweeping across northern Mali in the chaotic aftermath of a March 22 coup in the capital Bamako.

"They have raped Timbuktu today. It is a crime," said a source close to a local imam in Timbuktu, known as the 'City of 333 Saints'.

Witnesses said that the Islamists, who regard shrines as idolatrous, had destroyed the tombs of Sidi Mahmoud, Sidi Moctar and Alpha Moya.

In addition to three historic mosques, Timbuktu is home to 16 cemeteries and mausoleums, according to the UNESCO website.

A spokesman for the group, Sanda Ould Boumama, vowed: "Ansar Dine will today destroy every mausoleum in the city. All of them, without exception."

"This is tragic news for us all," Alissandra Cummins, chair of UNESCO's executive committee, said in a statement to AFP in Russia, where the body is meeting this week, describing the attacks as "wanton damage".

"I appeal to all those engaged in the conflict in Timbuktu to exercise their responsibility -- for the sake of future generations, spare the legacy of their past," she pleaded.

Mali's government in Bamako denounced the "destructive fury", comparing it to war crimes and threatened action on the national and international level.

Former colonial power France condemned 'the systematic violation of these places of reverence and prayer" and appealed "for an end to this violence and this intolerance'.

The destruction is reminiscent of the Taliban blowing up the giant Buddhas of the Bamiyan valley in Afghanistan - an ancient Buddhist and world heritage site on the Silk Road - in March 2001 after branding them un-Islamic.

'They shouted Allahu Akbar'

A witness said that early Saturday morning, about '30 fighters of Ansar Dine moved towards the mausoleum of Sidi Mahmoud' in the city's north.

"Some had guns. They did not shoot. Then they started shouting 'Allahu Akbar! Allahu Akbar!' (God is greatest! God is greatest!) And with pick-axes and hoes, they started to break down the mausoleum."

The Ansar Dine spokesman suggested Saturday's action was in retaliation for a UNESCO decision Thursday to put the World Heritage site, a cradle of Islamic learning founded in the fifth century, on its endangered list.

"God is unique. All of this is haram (forbidden in Islam). We are all Muslims. UNESCO is what?" he said, declaring that Ansar Dine was acting 'in the name of God'.

UNESCO's general director Irina Bokova confirmed that Islamist militants from the Ansar Dine group have destroyed three sacred tombs in Timbuktu, declaring in a statement that "there is no justification for such wanton destruction."

Witnesses in Timbuktu said that the gangs had destroyed the mausoleum of a saint whose 15th century tomb was already desecrated in May by members of Al-Qaeda in the Islamic Magreb (AQIM), another of the groups in control in the north.

The UN cultural agency said its decision to place both the town and the nearby Tomb of Askia in Gao on its List of World Heritage in Danger 'aims to raise cooperation and support for the sites threatened by the armed conflict'.

Mali has been gripped by chaos since disgruntled troops swarmed Bamako in the south in March and ousted the elected president of what had been seen as one of Africa's model democracies.

Islamist and tribal Tuareg groups seized on the power vacuum and pushed government forces out of northern Mali - an area the size of France and Belgium - including Timbuktu and the cities of Gao and Kidal.