Greece has confirmed that it will not facilitate the voyage of an Iranian oil tanker to Syria, after the U.S. warned Athens against allowing the vessel to dock at a Greek port.

The Adrian Darya 1 is at the centre of a row between Tehran and Washington, over allegations that it is transporting Iranian oil to Syria in violation of European Union sanctions.

The vessel was scheduled to arrive at Kalamata port in Greece on 26 August after leaving Gibraltar - where it had been held for five weeks - on 18 August.

After the detention order was lifted, the U.S. demanded the seizure of the vessel on the grounds that it was linked to Iran's Revolutionary Guards, but that was rejected by Gibraltar.

Greece's Deputy Foreign Minister, Miltiadis Varvitsiotis, told the ANT1 TV station that Athens had been "pressured" by the U.S. not to aid the vessel in any way.

"We want to send a message that we are not willing to facilitate the course of this ship to Syria," Varvitsiotis said.

He added that due to the ship's size, it was unlikely that it would be able to dock at a Greek port, but that "the ship can enter Greek territorial waters or anchor somewhere.”

Tehran has warned Washington that any attempt to seize the Adrian Darya 1 would have "heavy consequences".

Oil sales to Syria are banned by the European Union, while Iranian oil sales are under sanction by the U.S.