The sources, who spoke on condition of anonymity, said Turkish anti-narcotics police received a tip off about the existence of a "large amount" of opiate drugs in a container coming from Syria in Piraeus port.
A special team was sent to Greece to share the intelligence report with Greek police.
In a joint operation, Turkish and Greek police searched a container at the port and seized opiate drugs.
The operation is ongoing and police is on the lookout for more suspects, the sources added.
Last month, Greece seized drugs worth more than 100 million Euros hidden aboard the Assad regime-flagged ship “Noka.”