ISIS madmen blew up two Muslim burial sites in the ancient Syrian city of Palmyra, stoking fears that its famous pillared temple could be next to fall, officials said Tuesday.

The IS group consider mausoleums to be a violation of their strict interpretation of Islamic law, and have regularly destroyed them in areas they control in Iraq and Syria.

Maamoun Abdulkarim, Syria’s head of antiquities, noted the veracity of the reports of Islamic State placing bombs in Palmyra, and said that “The city is a hostage in their hands, the situation is unsafe”.

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

“All tombs with marble designs were destroyed”.

The men killed in the latest video are said to be “spies”, with some of them making recorded “confessions”.

IS, which controls swathes of territory across Syria and Iraq where it has created a self-proclaimed “caliphate”, advocates an extreme view of the application of Islamic law, or sharia.

On the same day, the United Nations cultural agency, UNESCO, warned that ISIL’s demolition of the world heritage site would be an “enormous loss to humanity”.

Numerous shrines destroyed by IS belonged to the Sufi sect, a mystical school of Islam despised by the Salafis who make up Islamic State, al-Nusra Front, al-Qaeda and similar groups.

On Sunday, the Islamic State group (IS/ISIS) planted large deal of explosives and mines in the archaeological locations of the Syrian ancient city of Palmyra (Tadmur), as a prelude to detonate them.

The ancient city can be traced back to 2000 BC and the desert oasis later became a key stop along the Silk Road, linking the known West to Asia.