An Iranian supertanker hauling 130 million dollars (£107 million) worth of crude oil that the US suspects is tied to a sanctioned organisation has left Gibraltar and is heading east into the Mediterranean Sea.

Its next destination is reported to be Greece.

The Iran-flagged Adrian Darya 1, previously named Grace 1, set course for Kalamata, Greece, with an estimated arrival of August 25, according to ship tracking service MarineTraffic.

The vessel left Gibraltar late on Sunday after having been detained for a month in the British overseas territory for allegedly attempting to breach European Union sanctions on Syria.

Gibraltar authorities rejected attempts by the US to seize the oil tanker again, arguing that EU regulations are less strict than US sanctions on Iran.

Gibraltar said it had been assured by Iran that the tanker would not unload its cargo in Syria.

GAuthorities in Gibraltar rejected the United States’ latest request not to release the supertanker
Authorities in Gibraltar rejected the United States’ latest request not to release the supertanker (Marcos Moreno/AP)

Iranian government officials have yet to publicly acknowledge the ship’s next destination, or where it will discharge its cargo of 2.1 million barrels of crude oil. Iran has denied it was ever headed for Syria.

The tanker’s release comes amid a growing confrontation between Iran and the West after US President Donald Trump pulled Washington out of Tehran’s nuclear deal with world powers over a year ago.

Shortly after the tanker’s detention in early July, Iran seized the British-flagged oil tanker Stena Impero, which remains held by the Islamic republic. Analysts had said the Iranian ship’s release by Gibraltar might mean that the Stena Impero could go free.

But Iranian officials denied there was any link between the two ships.

“There is no specific relation between these two ships,” said Foreign Ministry spokesman Abbas Mousavi of the Stena Impero and the Adrian Darya 1. “We are glad that our stance about the unlawful and illegal seizure of our tanker has been proven.”

Crew members of the Grace 1 remove the name of the ship
Crew members of the Grace 1 remove the name of the ship (Marcos Moreno/AP)

“Regarding the release of the law-breaking British tanker (Stena Impero), we have to wait for the court’s ruling,” he added. “This tanker has committed two to three nautical violations that are being investigated. We hope that these investigations will finish as soon as possible and a verdict will be issued and if the verdict orders its release, it can continue to sail its path.”

In a last-ditch effort to stop the release, the US unsealed a warrant on Friday to seize the Adrian Darya 1 and its cargo, citing violations of US sanctions as well as money laundering and terrorism statutes.

US officials told reporters that the oil aboard the ship was destined for a designated terror organisation.

The unsealed court documents argued that Iran’s Islamic Revolutionary Guard Corps are the ship’s true owners through a network of front companies.

Authorities in Gibraltar said on Sunday that, unlike in the US, the Revolutionary Guard is not designated a terrorist organisation under EU, UK or Gibraltar law.

The Iranian spokesman warned on Monday against any order by the US Justice Department to have the renamed ship seized again.

“If such an action is taken or even if it is stated verbally and not done, it is considered a threat against the maritime security in international waters,” said Mr Mousavi.

“The Islamic Republic of Iran has given necessary warnings to the US officials through official channels, especially the Swiss embassy in Tehran, not to commit such a mistake which (could) bring them severe consequences.”

The Iranian ship was detained while sailing under a Panamanian flag with the name Grace 1. It changed the name on Sunday and hoisted an Iranian flag.