BAMAKO, Mali (Reuters) — Ignoring international calls to halt their attacks, Islamist militants in Timbuktu continued to smash the mausoleums of Sufi saints on Sunday, witnesses said.

The hard-line Salafi group Ansar Dine, which supports a puritanical version of Islamic law, consider the centuries-old Sufi shrines in Timbuktu to be idolatrous. About 30 militants armed with assault rifles and pickaxes destroyed three mausoleums on Saturday and three more on Sunday, witnesses said. The group said it planned to destroy all 16 of the city’s main shrines.

The United Nations’s cultural agency Unesco recently put Timbuktu on its list of endangered world heritage sites, fearing damage to landmarks and cultural treasures in the wake of a coup in March. But the militants have ignored its call to halt the attacks.

“We are subject to religion and not to international opinion,” said an Ansar Dine spokesman, Oumar Ould Hamaha. “Building on graves is contrary to Islam.”