MADRID, Spain (AP) — Authorities in Gibraltar said they intercepted an Iranian supertanker yesterday that was believed to be breaching European Union sanctions by carrying a shipment of Tehran’s crude oil to war-ravaged Syria.

A senior Spanish official said the operation was requested by the United States. Iran’s state-run IRNA news agency called the incident “an illegal seizure of an Iranian oil tanker”.

Gibraltar port and law enforcement agencies, assisted by Britain’s Royal Marines, boarded the Grace 1 early yesterday, authorities on the British overseas territory at the tip of Spain said in a statement.

It added that the vessel was believed to be headed to the Baniyas Refinery in Syria, a government-owned facility under the control of Syrian President Bashar Assad and subject to the EU’s Syrian Sanctions Regime.

The EU and others have imposed sanctions on Assad’s government over its continued crackdown against civilians. They currently target 270 people and 70 entities.

Spain’s caretaker foreign minister, Josep Borrell, said the tanker was stopped by British authorities after a request from the United States.

Iranian Foreign Ministry spokesman Abbas Mousavi said in a tweet that British Ambassador Rob Macaire was summoned over the “illegal interception” of the ship. Mousavi later called the ship’s seizure “odd and destructive”.

“It can cause an increase in tensions in the region,” he said in a live telephone interview on state television yesterday.

US national security adviser John Bolton tweeted that the ship’s seizure was “excellent news”.

“America and our allies will continue to prevent regimes in Tehran & Damascus from profiting off this illicit trade,” Bolton added.

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 argues that it is not, and the tanker operation risks offending the Spanish.

“We’re looking into how this (operation) affects our sovereignty,” said Borrell, who was nominated earlier this week to become the EU’s foreign policy chief.