Archeological sites in Syria are being looted "on an industrial scale," with proceeds being used to fund Islamic State extremists.

Archeological sites in Syria are being looted "on an industrial scale," with proceeds being used to fund Islamic State extremists, the head of UNESCO warned Wednesday.

"Satellite imagery shows that archeological sites in Syria are dotted by thousands of illegal excavations... that show there is looting on an industrial scale," Irina Bokova said in Sofia.

"Limiting the trafficking in cultural property is a top priority because it finances the actions of the extremists," she told a news conference.

"The world expects from us to undertake decisive and uncompromising actions... to stop this source of funding for the extremists."

In four years of terrorist attacks by the so-called 'Islamic State of Iraq and the Levant' (ISIL) takfiri group, the Association for the Protection of Syrian Archaeology (APSA) says that more than 900 monuments and archeological sites have been looted, damaged or destroyed.

The terrorist operatives have blown up several famed tower tombs at the UNESCO-listed world heritage site of Palmyra, which they captured in May.

In August, they murdered the 82-year-old retired head of antiquities in Palmyra, Khaled al-Assad, and hung his mutilated body in public.

Bokova said the destruction at Palmyra "is an impudent crime against civilization because it was a symbol of cultural dialogue, a material proof of the ability of cultures to interact... This is what the extremists are seeking to destroy."