DAMASCUS (AFP) - Islamic State in Iraq and Syira (ISIS) fighters have destroyed two ancient Muslim mausoleums in the historic Syrian city of Palmyra, the country's antiquities director said on Tuesday.

Mr Maamoun Abdulkarim said ISIS militants blew up the tombs of Mohammed bin Ali, a descendant of Prophet Muhammad's cousin, and Nizar Abu Bahaaeddine, a religious figure from Palmyra, three days ago.

Bin Ali's burial place is located in a mountainous region 4km north of Palmyra, in central Syria.

Photos published by ISIS depicted two armed men carrying cannisters, apparently filled with explosives, walking up the rocky hill to the site.

Abu Bahaaeddine's tomb, nestled in a leafy oasis about 500m from Palmyra's ancient ruins, is said to be more than five centuries old.

ISIS has destroyed at least 50 mausoleums dating between 100 and 200 years old in the regions under its control in north and east Syria, the antiquities director said.

"They consider these Islamic mausoleums to be against their beliefs, and they ban all visits to these sites," Mr Abulkarim said.

Ten days ago, fighters from the militant group also destroyed a number of tombstones at a cemetery for Palmyra residents, Mr Abulkarim told AFP.

"All tombs with marble designs were destroyed. For them, graves should not be visible," he said.

The extremist group captured Palmyra, a renowned Unesco World Heritage site, from pro-government forces on May 21.

At the weekend, ISIS fighters mined the city's ancient site, renewing fears that they would demolish the famed ruins as they have other historic sites in Iraq.

Syria's army has advanced in recent days west of the city, near key oil and gas fields.