(CNN) -- Members of two Islamist militant groups destroyed tombs at a shrine to Muslim saints Tuesday, according to the mayor of Timbuktu, Mali, and other residents.
"The Islamists ordered the people to leave the area before they started smashing the tombs," Mayor Ousmane Halle said. "I saw both members of Ansar Dine and MUJAO, another Islamic faction in charge of the city. They were heavily armed and people had no choice but to leave when they started destroying the shrines."
It was the second time in the past two weeks that Ansar Dine, a militant group that seeks to impose strict Sharia law, has attacked the site's 16 mausoleums, built from mud and wood in the 15th century.
One of the town's residents said the militants surrounded the ancient Djingareyber mosque area at 7:30 a.m.
"They were shooting in the air to warn people of going near and entering the area," Allimam Oumar said. The militants think the shrines are idolatrous, he said.
The tombs are part of a newly designated UNESCO World Heritage site.
Mali was plunged into chaos by a military coup in March that ousted former President Amadou Toumani Toure. Since then, the Tuareg rebels and the Islamists have taken advantage of the uncertainty to attempt to seize control of the northern portion of the nation.
Last week, the United Nations called for sanctions against Islamist fighters in northern Mali and warned it is considering a proposal by West Africa states to deploy troops in the troubled country.