The Turkish government is coming under renewed pressure to stop buying gold from Venezuela.
Turkey is now considered the main concern among the countries engaging in the trade.
There are growing suspicions that gold exported to Turkey is ending up in Iran, which would violate US sanctions.
Turkish President Recep Tayyip Erdogan has sided strongly with Venezuelan President Nicolás Maduro, who is facing a growing political challenge.
Venezuela’s gold trade with Turkey is soaring. Last year, the country exported almost $900m (£688m) worth of gold to Turkey, ostensibly to be refined there and returned to Venezuela, although there is no record of re-exportation.
So the suspicion is growing that some of the gold may be heading via Turkey to Iran, which would violate US sanctions.