The International Criminal Court has threatened Islamist fighters in Mali with legal action if they do not halt their destruction of ancient Islamic monuments.

"My message to those involved in these criminal acts is clear: stop the destruction of the religious buildings now," Chief Prosecutor Fatou Bensouda told the AFP news agency in an interview. "This is a war crime which my office has authority to fully investigate."

She said that Mali was a signatory to the Rome Statute, a document that established the ICC and states that deliberate attacks against undefended civilian buildings which are not military objectives are a war crime.

"This includes attacks against historical monuments as well as destruction of buildings dedicated to religion," Bensouda said.

Members of the group Ansar Dine have destroyed the mausoleums of Sufi saints in historic Timbuktu for two straight days.

Yaya Tandina, a local journalist, told the Reuters news agency that about 30 members of the group, armed with Kalashnikovs and pickaxes destroyed three mausoleums of saints on Sunday.

"They had armed men guarding the door. Just like yesterday, the population did not react. They said we need to let them do what they want, hoping that someday we will rebuild the tombs," Tandina said.

Seven ancient tombshave been smashed by Ansar Dine since Saturday. The group's strict interpretation of Islam considers such places unholy and calls for their destruction.

The demolitions began on Saturday with Timbuktu's independence monument, which depicts Al Farouk, a symbol of the ancient city on a horse.

Ansar Dine have also threatened to destroy the city's three ancient mosques, one of which dates back to 1327.

Sanda Ould Boumama, an Ansar Dine spokesman, has said the group was acting in the name of God and would "destroy every mausoleum in the city. All of them, without exception".

The destruction comes after UNESCO listed the city as an endangered site because of the continuing violence in northern Mali and in the wake of an attack on a fifteenth century tomb in May.

"God is unique. All of this is haram [forbidden]. We are all Muslims. UNESCO is what," said Boumama.

The government of Mali has urged the outside world to take concrete steps to stop the destruction of the sites.

"Those who are destroying religious buildings in Timbuktu should do so in full knowledge that they will be held accountable and justice will prevail," she said.