THE detention of an Iranian oil tanker off Gibraltar was a threatening act that will not be tolerated, Iran’s Defence Minister Amir Hatami was cited by Reuters as saying in a televised address.

Very large crude carrier Grace 1 was boarded and seized by officials backed by Royal Marines on July 4 on suspicion it was carrying oil to Syria in violation of European Union sanctions.

The following day, the government of Gibraltar said it had been granted a Supreme Court order allowing for the vessel to be held for up to 14 days.

Iran denies the vessel was headed to Syria, where the government of President Bashar al-Assad is an ally of Tehran.

Iran’s Deputy Foreign Minister Abbas Araqchi said on Sunday the tanker was not headed to Syria. He did not specify the final destination. He said that no port in Syria is capable of docking the vessel — which is 1,000ft long — and it was therefore not violating EU sanctions, as Britain has claimed.

“These days we witnessed a threatening act from the government of England in the Strait of Gibraltar against a tanker from the Islamic Republic of Iran,” Mr Hatami said today on state television, according to Reuters.

“This is an incorrect and wrong action, an action similar to maritime robbery...certainly these kind of robberies will not be tolerated.”

On July 5, Mohsen Rezaei, a member of a council that advises the Supreme Leader Ayatollah Khamenei, said in a Twitter post that Iran would respond to bullies “without hesitation”.

He added: “If Britain does not release the Iranian oil tanker, it is the authorities’ duty to seize a British oil tanker.”

The seizure of Grace 1 comes at a politically sensitive time. The European Union has only just launched a financial trading instrument designed to circumvent US sanctions on Iran in an attempt to save the nuclear deal.

Spain’s acting foreign minister Josep Borrell said the mission was actually carried out at America’s request, implying that the raid had little to do with EU sanctions.