It's now called the Adrian Darya 1 and Iran's ambassador to London said it was expected to leave Gibraltar sometime on Sunday night.
On Sunday, video footage and photographs showed the tanker flying the red, green and white flag of Iran and bearing its new name, painted in white, on the hull.
British Royal Marines seized the vessel in Gibraltar in July on suspicion that it was carrying oil to Syria, a close ally of Iran, in violation of European Union sanctions.
The Iranian ship was detained while sailing under a Panamanian flag with the name Grace 1.
Gibraltar has rejected a request by the USA to again seize an Iranian tanker that it has been holding since July on suspicion of transporting oil to Syria.
The British overseas territory rejected a warrant issued Friday by a federal court in Washington that sought the supertanker's arrest, the oil it carried and the nearly $1 million found on board.
In a last-ditch effort to stop the release, the US unsealed a warrant Friday to seize the vessel and its cargo of 2.1 million barrels of light crude oil, citing violations of USA sanctions as well as money laundering and terrorism statutes.
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The US Department of Justice had requested that a new legal procedure for the detention of the tanker be commenced on the grounds that it has links to Iran's Islamic Revolutionary Guard Corps (IRGC), which it designates as a terrorist organisation.
It said: "The EU sanctions regime against Iran - which is applicable in Gibraltar - is much narrower than that applicable in the USA".
Gibraltar said on Sunday it could not comply with that request because it was bound by European Union law.
Iran's navy commander, Rear Adm. Hossein Khanzadi, offered to dispatch the Iranian navy to escort the Adrian Darya 1, according to Iran's Mehr news agency.
Gibraltar's government announced this week it was releasing the supertanker despite pressure from the United States for the vessel's continued detainment.
That prompted Iran to seize a British flagged tanker in the Persian Gulf in retaliation a fortnight later and sparked a crisis in diplomatic relations between the two countries.
That tanker, the Stena Impero, is still detained.
The Gibraltar court ruled that the American sanctions on Iran, which were imposed by President Trump after he walked away from the Iran nuclear deal previous year, do not apply in the European Union.