Islamist militants are tearing down more ancient mausoleums in the northern Malian city of Timbuktu.

Witnesses and tourism officials say rebels from the Ansar Dine group began destroying the mausoleums Sunday with pickaxes.

The militants destroyed several mausoleums in the city in July, after the U.N. cultural agency, UNESCO, put Timbuktu on its list of sites that are in danger.

UNESCO has listed Timbuktu as a World Heritage site for its ancient mosques and shrines, some of which date back to the 15th century.

The sites are revered by many Muslims but Ansar Dine considers them sacrilegious.

Ansar Dine is one of three militant groups that seized control of northern Mali earlier this year, after renegade soldiers overthrew the government.

The groups are trying to enforce a strict form of Islamic law across the territory. The U.N. and human rights groups have condemned the militants for abuses that include amputations and floggings of alleged criminals.

On Thursday, the United Nations Security Council has authorized the deployment of foreign troops to Mali.

The Economic Community is making plans to send a force of between 3,000 and 4,000 soldiers to retrain the Malian army and help retake the north.