The Iranian oil tanker Adrian Darya 1 at the centre of a dispute between Tehran and western powers has been photographed by satellite off the Syrian port of Tartus, a US space technology company has said.

Maxar Technologies Inc said the image showed the tanker Adrian Darya 1 very close to Tartus on 6 September. The ship appeared to have turned off its transponder in the Mediterranean west of Syria, ship-tracking data showed. The tanker, which is loaded with Iranian crude oil, sent its last signal giving its position between Cyprus and Syria sailing north on Monday afternoon.

The vessel, formerly named Grace 1, was detained by British Royal Marine commandos off Gibraltar on 4 July as it was suspected to be en route to Syria in violation of EU sanctions. Iran in retaliation seized a British-flagged tanker in the Strait of Hormuz leading into the Gulf.

Gibraltar released the Iranian vessel on 15 August after receiving written assurances from Tehran that it would not discharge its 2.1m 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. The US treasury blacklisted the tanker on Friday.