The reports says the trade has raised tens of millions of dollars for ISIS, a sum comparable to the profit the terrorists have made by the kidnap and ransom of Western hostages.

Since its attck to Syria and Iraq last year, ISIS has sought to transform itself into an organisation capable of ruling its own state, setting up an elaborate hierarchy of leadership and ministries.

But while elsewhere in the Middle East, ministries of this kind try to protect antiquities; ISIS version was established to pillage and smuggle these treasures in a territory replete with classical ruins.

"They happened upon a pre-existing situation of looting and turned it into a highly organised trade," said Amr al-Azm, a former official in the Syrian antiquities ministry who now runs a network of archaeologists and activists to document the destruction of the country's treasures.

In Iraq, ISIS elements have desecrated and looted the Assyrian remains at Mosul, Nimrud and Hatra.

Earlier this month, they captured the Roman city of Palmyra in Syria, raising fears that it might suffer the same treatment.