Armed fighters of Mali's al Qaeda-linked Ansar Dine Islamist group have destroyed mausoleums in the ancient trading city of Timbuktu.

The city has been classified as a UNESCO World Heritage site.

The attack came just four days after UNESCO agreed to a request to place Timbuktu on its list of heritage sites in danger after the seizure of its northern two-thirds in April by rebels.

Witnesses said the mausoleum of Sidi Mahmoud (Ben Amar) and two others have been completely destroyed.

Since government forces were routed in April, Ansar Dine and other Islamist groups with links to al-Qaeda in the Islamic Maghreb (AQIM) have gained the upper hand over less well-armed Tuaregs whose goal is a secular, independent northern state.

Ansar Dine is pushing for strict sharia, Islamic law, across the whole of the country.

It deems un-Islamic the shrines of Timbuktu, an expression of the local Sufi brand of the religion.