The Islamist Ansar Dine group backs strict sharia, Islamic law, and considers the shrines of the local Sufi version of Islam to be idolatrous. Sufi shrines have also been attacked by hardline Salafists in Egypt and Libya in the past year.

The attack came just days after UNESCO placed Timbuktu on its list of heritage sites in danger and will recall the 2001 dynamiting by the Taliban of two 6th-century statues of Buddha carved into a cliff in Bamiyan in central Afghanistan.

"They are armed and have surrounded the sites with pick-up trucks. The population is just looking on helplessly," local journalist Yeya Tandina said by telephone.

Tandina and other witnesses said Ansar Dine had already destroyed the mausoleums of three local saints - Sidi Mahmoud, Sidi El Mokhtar and Alfa Moya - and at least seven tombs.

"The mausoleum doesn't exist anymore and the cemetery is as bare as a soccer pitch," local teacher Abdoulaye Boulahi said of the Mahmoud burial place.

"There's about 30 of them breaking everything up with pick-axes and hoes. They've put their Kalashnikovs down by their side. These are shocking scenes for the people in Timbuktu," said Boulahi.

Contacted late on Saturday, Tandina said Ansar Dine had halted the attacks on the holy site. Attempts to contact members of the group were unsuccessful.

Locals said the attackers had threatened to destroy all of the 16 main mausoleum sites by the end of the day. UNESCO Director-General Irina Bokova called for an immediate halt.