Iran has sold the oil on the tanker which was detained by Royal Marines off Gibraltar, an Iranian government spokesperson has said.
Iran did not say who it had been sold to but requested that the tanker be sent to the recipient.
The tanker, now called Adrian Darya 1 but formerly known as Grace 1, was released on 18 August by Gibraltar after weeks in the custody of British Royal Marines.
It had been detained because it was suspected it was delivering oil to Syria, which is a breach of international sanctions.
The Trump administration, which said the tanker was transporting around £130m worth in light crude, attempted to block the release of the tanker but failed.
America has a warrant out for the ship and has warned nations not to accept it.
After setting out from Gibraltar, the Adrian Darya first navigated to Greece, which refused to let it refuel.
It was then destined for Turkey but Refinitiv Eikon shipping data showed on Monday that the tanker was no longer headed in that direction.
It is not clear where the tanker is now travelling to, but appears to be going east in the Mediterranean Sea.
The seizure of the ship off Gibraltar led to Iran detaining the British-flagged Stena Impero in the Gulf, something Jeremy Hunt, the then foreign secretary, called “an act of state piracy”.
The Stena Impero is still being held.
Tensions have been high between the US and Iran, with America backing out of the Iran nuclear deal (which Britain, France and other countries remain committed to) and sending more military assets to the Persian Gulf.
Among other actions, the US has hit Iran’s economy by re-imposing and creating new sanctions blocking Tehran from selling crude oil aboard, and declaring the Islamic Revolutionary Guard Corps, a branch of government forces, a terror organisation.
US President Donald Trump said on the sidelines of the G7 Summit that he was not looking to see a change in leadership in Tehran.
He said he wanted a strong Iran, just one that was not nuclear or engaging in terrorism.
He said: “I’m looking at a really good Iran, really strong, we’re not looking for regime change. You’ve seen how that works over the last 20 years, that hasn’t been too good.”
His comments came shortly after the Iranian foreign minister Mohammad Javad Zarif made a surprise appearance at the summit, something Mr Trump was reportedly tipped off to shortly before.
“I knew he was coming in and I respected the fact that he was coming in. And we’re looking to make Iran rich again, let them be rich, let them do well, if they want,” Mr Trump said.
“Or they can be poor as can be. And I tell you what, I don’t think it’s acceptable the way they are being forced to live in Iran,” he said.
He added: “What we want is very simple. It’s got to be non-nuclear. We’re going to talk about ballistic missiles, we’re going to talk about the timing… But they have to stop terrorism. I think they are going to change, I really do. I think they have a chance.”