The spokesman for Iran's Foreign Ministry says despite all acts of sabotage by the United States, the Iranian tanker Adrian Darya 1 has discharged its oil cargo and is now berthing at a Mediterranean port.
The Stena Impero was going through the final legal processes and would be released "soon", spokesman Abbas Mousavi said.
In retaliation, Iran seized a British-flagged tanker in the Strait of Hormuz leading into the Gulf.
The seizure of the Stena Impero was seen as a tit-for-tat move after British authorities detained an Iranian tanker off Gibraltar in July on suspicion it was shipping oil to Syria in breach of European Union sanctions.Tehran denied it had made any promises about the destination of the ship laden with 2.1 million barrels of oil, which had been elusive since leaving Gibraltar.Maritime tracking service TankerTrackers said that as of Sunday night the Adrian Darya was off the coast of Syria's Tartus but had not unloaded the oil.
Iran insisted the ship and its 2.1million barrels of oil were not headed for Syria, but fears have grown since the tanker turned its tracker beacon off last week.
The ship, originally known as Grace 1 when it was detained in July off Gibraltar, a British territory, has been a further cause of tension between Washington and Tehran.
However, sources in the shipping sector suggest that the tanker is trying to transfer part of its cargo to another ship, after Iran said it sold the oil.
The US past year withdrew from the global 2015 deal to limit Iran's nuclear programme, and reinstated sanctions.
The EU has sought to salvage the accord.
"The ship is somewhere in the Mediterranean, has already sold its oil on board and the owner will now decide how to proceed with the tanker", Mussawi said but did not elaborate to whom the oil was sold.
The US Department of Justice issued a warrant for the seizure of the ship, and the US Department of State has confirmed that US officials subsequently offered the ship's Indian captain millions to take the ship's oil to a port where the oil - worth as much as as £110m - could be impounded by the US. After the captain gave no positive response, he and the ship were put under U.S. sanctions.
Media affiliated with the Syrian regime in Tartus welcomed the Iranian tanker, and thanked Iran for "defying the whole world and US".
Following the emergence of the satellite images on Saturday, the UK's Foreign Office called the reports of the ship's presence near Syria "deeply troubling".