TEHRAN – An Iranian oil tanker was seized by Gibraltar police, aided by a detachment of British Royal Marines, on Thursday.

Grace 1, a supertanker, was boarded and impounded by Gibraltar police following U.S. request in the Strait of Gibraltar, sources reported.

Following the seizure, the British Ambassador to Tehran, Robert Macaire, was summoned to the Foreign Ministry in the evening of Thursday in protest over the “illegal” seizure.

The Foreign Ministry described the move as “unacceptable” and called for an immediate release of the tanker, given that it has been seized at the request of the U.S. based on the information currently available, the ministry said in a report on its website.

Pointing to the fact that the oil tanker was sailing in international waters, Iran called the UK Navy’s move “tantamount to maritime banditry”, and stressed that Britain has no right to impose its own unilateral sanctions or those of the European Union in an extraterritorial manner against other countries.

This is the very bullying policy of the U.S., about which the European countries have been always protesting, the ministry said.

The ambassador was provided with the document about the oil tanker and its cargo indicating the ship’s completely legal passage.

It was also emphasized that Iran will be using all its political and legal capacities to secure the release of the vessel and uphold its rights.

The UK ambassador said he will immediately convey the protest to London, stressing that his country does not follow the unilateral U.S. sanctions against Iran.

Spain’s caretaker foreign minister, Josep Borrell, who was nominated this week to become the EU’s foreign policy chief, said the tanker was stopped by British authorities after a request from the United States.

In Madrid, Borrell told reporters that Spain was assessing the implications of the operation because the detention took place in waters it considers its own.

Britain insists Gibraltar is part of the United Kingdom but Spain says it is not, and the tanker operation risks offending the Spanish.

“We’re looking into how this (operation) affects our sovereignty,” said Borrell.

A spokesman for British Prime Minister Theresa May said she welcomed the “firm action” by the authorities in Gibraltar.

“We have reason to believe that the Grace 1 was carrying its shipment of crude oil to the Banyas Refinery in Syria,” Gibraltar’s chief minister, Fabian Picardo, said in a statement.

John Bolton, White House national security adviser, applauded the interception of the supertanker.

“Excellent news: UK has detained the supertanker Grace I laden with Iranian oil bound for Syria in violation of EU sanctions,” Bolton said on Twitter, according to Al Jazeera.

SP/PA