Such "cultural cleansing" was also a source of financing for militants, UNESCO says

Islamic State militants are looting ancient sites across Iraq and Syria on an industrial scale and selling on treasures to middlemen to raise cash, Irina Bokova, the head of the U.N. cultural agency, UNESCO, said.

One fifth of world-renowned sites under Islamic State control are heavily looted, and it was unclear what is happening in "thousands more" areas, Ms. Bokova told.

Some sites in Syria had been ransacked so badly that they no longer have any value for historians and archaeologists, and UNESCO is also increasingly worried about Libya, she said.

Islamic State's self-declared caliphate contains some of the richest archaeological treasures on earth, in a region where ancient Assyrian empires built their capitals, Greco-Roman civilisation flourished, and Muslim and Christian sects co-existed for centuries.

The militants, whose strict ‘Salafi’ interpretation of Islam deems the veneration of tombs and non-Islamic vestiges to be idolatrous, had also posted videos of themselves destroying artefacts.

"The deliberate destruction, what we are seeing nowadays in Iraq and Syria, has reached unprecedented levels in contemporary history," Ms. Bokova told the Royal United Services Institute (RUSI) in London.

"This deliberate destruction is not only continuing, it is happening on a systematic basis. The looting of archaeological sites and museums, in Iraq particularly, has reached an industrial scale of destruction,” she said.

Such "cultural cleansing" was aimed at destroying humanity's common roots, but was also a source of financing for militants who, she said, were charging local farmers to excavate sites and smuggling out artefacts which eventually made their way to private collectors around the world.

"Daesh (IS) knows there's a financial upside of this activity and they are trying to gain from it. We know also that parties in the conflict are selling to certain dealers and to private collectors and to market end buyers," she added.

Satellite images helped UNESCO understand what was going on, but in some areas there were just hundreds of holes in the ground from which artefacts were being extracted and it was difficult to understand what was being looted, she explained.