This is the first time Europe has seized a tanker at sea despite a ban on oil shipments to Syria since 2011.
LONDON — British Royal Marines seized an oil tanker in Gibraltar on Thursday accused of bringing oil to Syria in violation of EU sanctions, a dramatic step that could escalate confrontation between the West and Iran.
The Grace 1 tanker was impounded in the British territory at the mouth of the Mediterranean Sea after sailing around Africa from the Middle East.
Shipping data reviewed by Reuters suggests it had been loaded with Iranian oil off the coast of Iran, although its documents say the oil is from neighboring Iraq.
The authorities in Gibraltar made no reference to the source of the oil when they seized it under the authority of European sanctions against Syria that have been in place for years.
But the likelihood that the cargo was Iranian drew a link between the incident and a new U.S. effort to halt all global sales of Iranian crude, which Tehran has described as an illegal "economic war" against it.
European countries have tried to stay neutral in that confrontation, which saw the United States call off air strikes against Iran just minutes before impact last month, and Tehran amass stocks of enriched uranium banned under a 2015 nuclear deal.
In a statement, the Gibraltar government said it had reasonable grounds to believe that the Grace 1 was carrying its shipment of crude oil to the Baniyas refinery in Syria.
"That refinery is the property of an entity that is subject to European Union sanctions against Syria," Gibraltar Chief Minister Fabian Picardo said. "With my consent, our port and law enforcement agencies sought the assistance of the Royal Marines in carrying out this operation."
A spokesman for British Prime Minister Theresa May welcomed Gibraltar's move, though the incident could also signal some tensions within Europe.
Spain, which challenges British ownership of Gibraltar, said the action was prompted by a U.S. request to Britain and appeared to have taken place in Spanish waters. Britain's Foreign Office did not respond to a request for comment.
While Europe has banned oil shipments to Syria since 2011, it had never seized a tanker at sea.
"This is the first time that the EU has done something so public and so aggressive. I imagine it was also coordinated in some manner with the U.S. given that NATO member forces have been involved," said Matthew Oresman, a partner with law firm Pillsbury Winthrop Shaw Pittman who advises firms on sanctions.
"This is likely to have been meant as a signal to Syria and Iran — as well as the U.S. — that Europe takes sanctions enforcement seriously and that the EU can also respond to Iranian brinkmanship related to ongoing nuclear negotiations."
Iran has long been supplying its allies in Syria with oil despite such sanctions.
But U.S. sanctions have been tightened sharply since May, effectively forcing Iran off of mainstream crude markets, making it desperate for alternative ways to sell oil and more reliant on its tanker fleet to store supplies it cannot sell. The sanctions have also choked off Tehran's Syrian allies, causing fuel shortages in government-controlled areas.
Ship mapping records from data firm Refinitiv show that in the latest case the Grace 1 sailed to the Mediterranean around the southern tip of Africa, instead of via Egypt's Suez Canal. The 300,000-tonne Panamanian-flagged tanker is registered as being managed by Singapore-based IShips Management Pte Ltd. Reuters was unable to establish contact with them for comment.
It was documented as loading fuel oil in the Iraqi port of Basra in December, though Basra did not list it as being in port and its tracking system was switched off. The tanker then reappeared on tracking maps near Iran's port of Bandar Assalyeh, fully loaded.