n A senior Iranian official said on Friday that Tehran should seize a British oil vessel in case London refuses to release the Iranian oil tanker detained in Gibraltar.

On Thursday, British Royal Marines helped officials in Gibraltar to seize an Iranian supertanker “Grace 1” suspected of carrying oil to Syria, “in breach of EU sanctions”.

Iran later summoned the British ambassador to Tehran Rob Macaire to complain about what it said was a “form of piracy”, Press TV reported.

“If Britain does not release the Iranian oil tanker, it is the authorities’ duty to make a reciprocal move and seize a British oil tanker,” said Major General Mohsen Rezaei, a member of a council that advises the country’s Supreme Leader Ayatollah Khamenei, in a tweet. He said that “Iran will never hesitate to respond to bullies”.

Spain, which challenges the British ownership of Gibraltar, said the action was prompted by a US request to Britain and appeared to have taken place in Spanish waters.

According to the BBC, a team of about 30 marines —from 42 Commando — were flown from the UK to Gibraltar to help detain Grace 1 and its cargo, at the request of the Gibraltar Government.

Gibraltar said there was reason to believe the ship was carrying Iranian crude oil to the Baniyas Refinery in the Syrian Mediterranean port town of Tartous.

But Iran’s Foreign Ministry condemned the move as illegal and accused the UK of acting at the behest of the US.

The UK Foreign Office dismissed claims of piracy as “nonsense”. On Friday, a senior Iranian lawmaker said the seizure of the tanker was proof that the UK “lacks honour” and takes orders from the US.

Mostafa Kavakebian, who leads the Iran-UK parliamentary friendship group, tweeted that the seizure was “a form of piracy and illegal hostility towards Iran”.