The Iranian oil tanker seized by UK forces last month left Gibraltar on Sunday night, shipping data showed, hours after the British territory refused to detain the tanker further despite a US request.
It is unclear where the vessel is heading.
A federal court in Washington issued a warrant for the seizure of the tanker on Friday, a day after Gibraltar authorities said the vessel was free to leave.
But Gibraltar on Sunday rejected the US move to hold the tanker, saying it could not comply because it was bound by EU law.
It was detained for six weeks over suspicions that it was trying to take oil to Syria, in breach of EU sanctions.
The US warrant said the tanker, its oil cargo and $995,000 (Dh3.6 million) were subject to forfeiture based on breaches of the International Emergency Economic Powers Act, and bank fraud, money laundering and terrorism forfeiture statutes.
But Gibraltar said European laws did not provide grounds for complying with the warrant.
“The Central Authority’s inability to seek the orders requested is a result of the operation of EU law and the differences in the sanctions regimes applicable to Iran in the EU and the US,” the government said.
“The EU sanctions regime against Iran, which is applicable in Gibraltar, is much narrower than that applicable in the US.”
Hamid Baeidinejad, Iran’s ambassador to the UK, said the ship was expected to sail on Sunday night after two engineering teams were sent to Gibraltar.
The tanker was sailing under a Panamanian flag with a cargo of 2.1 million barrels of crude when it was seized by Royal Marines on July 4 in the waters of Gibraltar, a British overseas territory.
But Panama’s Maritime Authority said in July that it had delisted the vessel after an alert that indicated the ship had taken part in or was linked to terrorism financing.
It has raised an Iranian flag and has been renamed. Pictures of the vessel previously known as Grace 1 show the name Adrian Darya-1 painted on its hull.
Mr Baeidinejad rejected claims that the renaming was to avoid US sanctions, saying it was because it had been reflagged as Iranian and therefore should have an Iranian name.
“Naturally, with the registration of the ship in Iran, a new Iranian name was picked for it,” he wrote on Twitter.
There were doubts about the ship's ability to leave port after reports that it was in need of repairs and that its Indian captain had asked to be replaced.
“He doesn’t want to stay in command of the ship," the captain's lawyer told AP. "He wants to go home, because he wasn’t happy to go back and pick up the broken pieces.
“But he’s a professional skipper and needs to wait for a new crew to do a proper handover.”
The lawyer said the tanker had been due for repairs in Gibraltar even before it was seized and its detention had hindered the replacement of parts, making it unfit for a long voyage.
The US last week also threatened visa bans against the tanker's crew and anyone associated with its operations.
Washington has imposed wide-ranging sanctions on Iran since withdrawing last year from a pact that eased economic penalties in exchange for curbs on Tehran's nuclear programme.
US President Donald Trump said the nuclear accord, in which Britain, France, Germany, Russia and China were signatories, did not address Iran’s missile development and destabilising action in the region.
It is not clear where the tanker will go next but Gibraltar said it agreed to release the ship after being given assurances by Iran that its cargo would not be delivered to Syria. Iranian officials say they made no such commitment.
The seizure of the tanker started a diplomatic crisis between Britain and Iran.
It was followed two weeks later by Iran's seizure of a British-flagged tanker, the Stena Impero, as it was passing through the Strait of Hormuz.
