Syria's antiquities chief has accused Turkey of refusing to return looted objects from ancient heritage sites in Syria or to provide information about them, allegations denied by the Turkish government.
Damascus and Ankara have been at odds since the start of a rebellion against Syrian President Bashar al-Assad in 2011, with Turkey supporting armed groups fighting Assad's government.
More recently, Islamic State militants have declared a caliphate in territory they hold across Syria and Iraq and have destroyed monuments they consider pagan and sacrilegious.
One museum at the 2,000-year-old Roman city of Palmyra, a UNESCO World Heritage site the jihadi militants took over in May, has been turned into an Islamic State prison and courtroom, Syria's antiquities chief Maamoun Abdulkarim told Reuters.
Even more destructive for Syria's archaeological heritage are illicit excavations at sites such as Palmyra and the even older site of Mari, near the Iraqi border, he said.
Abdulkarim said more than 2,000 objects looted from these sites had been seized in Turkey, which in contrast to other countries neighboring Syria refuses to cooperate with the Syrian authorities on documenting and returning the artifacts.
"The Turkish government refuses to register (the seized objects). There is no information, no pictures. It's not transparent," Abdulkarim told Reuters in an interview in Vienna.
"They should change their approach. They told us, we cannot (do this) because our law (prohibits) us from declaring what we have," he said.
A Turkish Culture Ministry spokesman said Abdulkarim's allegations were "baseless".
"Some Syrian antiquities may have been smuggled to Turkey ... We are doing our best to prevent such smuggling," he said.
"Whenever we seize such antiquities we return them to the related country's institutions. We trained our border police on the issue very recently. I think those allegations are politically motivated," the Turkish official said.
Permits issued by Islamic State
The 2,000 objects seized in Turkey compare with 6,500 recovered by Syrian authorities from smugglers, 300 seized by Jordanian authorities and 90 returned to Syria from Lebanon since the beginning of the war, according to Abdulkarim.
He said that the absence of relations between Syria and Israel meant no information about looted objects found there was reaching him either.
Abdulkarim described permits issued to looters by Islamic State, also known as Daesh, in exchange for a cut of their profits. Equipped with these documents, looters could trawl sites such as Mari or nearby Dura Europos with bulldozers in search of artifacts to smuggle to Turkey.
"Last month we received these documents (that say) 'State of Daesh', the Department for Archeology gives this person the permission to do whatever excavation he wants at this site," Abdulkarim said.
Looting began on a large scale in 2013, and nothing has changed on the ground since a United Nations resolution protecting Syrian and Iraqi heritage sites passed in February, he said.
"We need European countries, the United States, Japan (and others) to convince those who buy our artifacts to refuse them," Abdulkarim said.
Buyers of such objects live in Britain, the United States, Arab Gulf countries, China, France, Germany and Switzerland, he said. "If you buy our artifacts, you support Daesh."