BEIRUT (REUTERS) - The Iranian oil tanker Adrian Darya 1 at the centre of a dispute between Teheran and Western powers appears to have turned off its transponder in the Mediterranean west of Syria, Refinitiv ship-tracking data showed on Tuesday (Sept 3).

The tanker which is loaded with Iranian crude oil, sent its last signal giving its position between Cyprus and Syria sailing north at 15.53 GMT Monday (11.53pm on Monday, Singapore time), the data showed.

The vessel, formerly named Grace 1, was detained by British Royal Marine commandos off Gibraltar on July 4, as it was suspected to be en route to Syria, in violation of European Union sanctions.

Two weeks later, Iran in retaliation seized a British-flagged tanker in the Strait of Hormuz leading into the Gulf.

Gibraltar released the Iranian vessel on Aug 15 after receiving formal written assurances from Teheran that the ship would not discharge its 2.1 million barrels of oil in Syria.

However, shipping sources say the tanker is likely to try to conduct a ship-to-ship transfer with another vessel for part of its cargo after Iran said a sale had been concluded.

Washington has warned any state against assisting the ship, saying it would consider that support for a terrorist organisation, namely, Iran's Islamic Revolutionary Guard Corps.

The US Treasury Department blacklisted the tanker last Friday.