Iran has sold 2.1 million barrels of oil aboard an Iranian tanker detained last month by Royal Marines in Gibraltar to a Lebanese firm, a source with knowledge of the matter told Iran International. 

The source said the owner of Adrian Darya 1, formerly known as the Grace 1, had sold its oil cargo, which was initially set to be destined to Syria, to the Lebanese firm at prices much lower than market rates. 

The source said Lebanon-based Syrian tycoon Samer Fayez, who is a close confidant of Syrian President Bashar Assad, had facilitated the disputed oil delivery.

The Lebanese government had already denied that the Adrian Darya 1 had docked in Lebanese ports. Lebanese Finance Minister Ali Hassan Khalil said on Friday he had no knowledge of the Arian Darya 1 heading towards his country.

Meanwhile, US Secretary of State Mike Pompeo said in a Twitter post on Friday: “We have reliable information that the tanker is underway and headed to Tartus, Syria”.

Pompeo noted that the Adrian Darya, which was formerly flying Panama’s flag, belonged to Iran’s Revolutionary Guards Corps (IRGC) which has been designated as a terrorist organization by the US.

Before Pompeo’s announcement, the US Treasury designated the Adrian Darya 1 as a "blocked property" using anti-terrorism rules crafted after the September 11 attacks. Treasury also blacklisted the vessel's master, identified as Capt. Akhilesh Kumar.

Iranian government spokesman Ali Rabiee said last Monday that the oil onboard the closely-watched tanker had been sold, without naming the buyer.

Asked about Fayez, Lebanese analyst Sami Nader told Iran International: “It is highly likely that people close to Bashar Assad’s regime would want to circumvent economic sanctions and embargo imposed against Syria by certain countries, headed by Europe and the US.”

Tartus is one of Syria’s key ports and is home to Russia’s largest military base which the Assad regime rented out to Moscow six months ago for a period of 49 years.

The Adrian Darya 1 was impounded in the waters off Gibraltar by British Marines on suspicion of carrying crude oil to Syria in violation of European Union sanctions. Iran dubbed the seizure “piracy”.

IRGC Navy forces reciprocated the measure by seizing a British tanker off the Strait of Hormuz, which remains still in detention.