Tehran has demanded the immediate release of the Grace 1 supertanker, which a detachment of Royal Marines boarded off the coast of Gibraltar on suspicion it was breaking European Union sanctions by carrying oil to Syria.
Hassan Rouhani called the seizure “mean and wrong” during a cabinet meeting, the official IRNA news agency reported.
“You [Britain] are an initiator of insecurity and you will understand its repercussions,” he warned, calling for the “full security” of international shipping lanes.
He added: “Now you are so hopeless that, when one of your tankers wants to move in the region, you have to bring your frigates [to escort it] because you are scared. Then why do you commit such acts? You should instead allow navigation to be safe.”
Meanwhile, Javad Zarif, Tehran’s foreign minister, denied the supertanker belonged to Iran.
He said whoever owned the oil shipment and the vessel could pursue the case through legal avenues.
Iran had earlier summoned the British ambassador over what it called the “illegal interception” of the ship.
Mapping data from Refinitiv Eikon released at the time the tanker was seized indicated it sailed from Iran via a route around the southern tip of Africa, rather than going through the Suez Canal in Egypt.
The Grace 1 was documented as loading fuel oil in Iraq in December, though the Iraqi port did not list it as being in port and its tracking system was switched off.
If the 300,000 tonne tanker was confirmed to be transporting Iranian crude oil, its attempted delivery to Syria could also be a violation of US sanctions on Iranian oil exports.
Iran, a key ally of Bashar al-Assad, Syria’s president, has been placed under heavy sanctions by the US after Donald Trump pulled out of the 2015 nuclear deal.
Tehran has offered to return to the agreement, but the US president has rejected the deal, arguing it was too generous to Iran and did not address its involvement in regional conflicts.
In May, the US dispatched an aircraft carrier, bombers and fighter jets to the Persian Gulf in response to alleged Iranian threats.
The US has also accused Iran of being involved in the bombing of oil tankers in the Gulf, and said it shot down an American drone in international airspace.
Iran has denied any involvement in the attacks on the tankers and said the drone had veered into its airspace.