This article is more than 1 year old

This article is more than 1 year old

Royal Marines have helped seize an Iranian supertanker suspected of carrying oil to Syria off the coast of Gibraltar, escalating tensions between the UK and Tehran as the agreement aimed at halting Iran’s nuclear programme unravels.

A detachment of nearly 30 British troops working with the Gibraltarian police intercepted the vessel, believed to be carrying 2m barrels of oil, in a dramatic manoeuvre Spain said had been conducted at the request of the US.

Tehran responded by summoning Britain’s ambassador to its foreign ministry to explain what it described as an “illegal seizure”, which had been earlier described by the UK as enforcing the EU’s sanctions regime against Syria.

It is understood that the ambassador, Rob Macaire, reiterated the British position during the meeting, saying: “[The UK] welcomes this firm action by the Gibraltarian authorities” to enforce sanctions against the regime of Bashar al-Assad.

Facebook Twitter Pinterest A Royal Marines vessel heads towards the Grace 1 supertanker near Gibraltar. Photograph: Marcos Moreno/AP

Marines from 42 Commando were involved in the overnight seizure, with some landing on the ship’s deck by rapidly descending down ropes suspended from a Wildcat helicopter, and the rest following up via speedboat.

A grainy black and white image from a thermal camera released by the Ministry of Defence on Thursday showed the helicopter hovering over one end of the ship, intercepted heading east through Gibraltarian waters.

Further colour pictures were released showing marines onboard Grace 1, whose ownership had not initially been clear, but whose origin was later confirmed by the Iranian foreign ministry.

Facebook Twitter Pinterest Royal Marine patrol vessel is seen beside Grace 1 super tanker off Gibraltar. Photograph: Marcos Moreno/AP

Its spokesman tweeted: “Following the illegal seizure of an Iranian oil tanker in Gibraltar by British Royal Marines, the UK envoy to Tehran has been summoned to the ministry of foreign affairs.”

MoD sources said British troops were at all times acting under the direction of the Gibraltar police. The marines provided the technical expertise to allow the tanker to be boarded at sea.

But the British position appeared to be contradicted by Spain, whose acting foreign minister, Josep Borrell, said Gibraltar had seized Grace 1 after a request from the US to Britain to pick up the tanker laden with crude oil.

The action comes at a time of heightened tensions between the US and Iran. Iran has been accused of sabotaging oil tankers in the strait of Hormuz, a policy of brinkmanship that analysts say is designed to show the US there is an economic cost to the Trump administration’s decision to pull out of the 2015 nuclear deal and impose economic sanctions.

White House national security adviser John Bolton welcomed the seizure of the ship. “Excellent news: UK has detained the supertanker Grace I laden with Iranian oil bound for Syria in violation of EU sanctions,” Bolton tweeted. “America & our allies will continue to prevent regimes in Tehran & Damascus from profiting off this illicit trade,” he said.

The UK Foreign Office faced a dilemma over the past few days knowing that if it seized the Iranian oil ship, as requested by the US, it risked deeply antagonising Tehran, which is desperate to increase its oil exports.

Iran, according to some officials, is now exporting as little 200,000 barrels per day, and needs that to be closer to 600,000 to keep its economy afloat.

But the Foreign Office reasoned that it had a legal and moral duty to impound any ship that was heading to Syria in breach of EU sanctions. It was the Iranian’s surprise decision to enter Gibraltarian waters with its communications transponders on that left the UK with the option to impound the vessel.

In making its decision, the UK had to weigh the possible knock-on effect on the Iran nuclear deal, as well as reprisals against British diplomats in Tehran that work in an embassy that was trashed by Iranian protesters in this century.

The UK insists it has no objections to Iran seeking to increase its oil exports, but only so long as it does not sell its products in breach of EU sanctions.

Facebook Twitter Pinterest A view of Grace 1 in Gibraltar. Syria is subject to EU sanctions due to the war in the country. Photograph: Marcos Moreno/AP

Officials were not sure how Iran would react to the British military action, but the decision to summon the UK ambassador is a signal that Tehran views the episode as proof that Britain is not truly committed to helping the Iranian economy weather the effect of secondary sanctions.

The 28 members of the ship’s crew were questioned onboard by Gibraltarian authorities. They were mostly Indian nationals but there were also some Ukrainians and Pakistanis, the territory’s government said.

Fabian Picardo, Gibraltar’s chief minister, thanked the efforts of the “brave men and women” from the marines and the local agencies involved in the operation, and confirmed Grace 1 had been detained.

“This action arose from information giving the Gibraltar government reasonable grounds to believe that the vessel, the Grace 1, was acting in breach of EU sanctions against Syria,” he said.

“In fact, we have reason to believe that the Grace 1 was carrying its shipment of crude oil to the Banyas refinery in Syria.”

Grace 1 was travelling east through the strait of Gibraltar. Tracking data from Lloyd’s List, a specialist shipping website, showed it had begun its voyage in Iran, travelling around Africa, before it passed through Gibraltarian territorial waters.

Mapping data showed it sailed a longer route to the mouth of the Mediterranean, around the southern tip of Africa, instead of via the Suez Canal in Egypt.

Panama’s Maritime Authority said on Thursday night that the ship was delisted from Panama’s international boat registry as of 29 May after it received an alert indicating that the Grace 1 had participated in or was linked to terrorism financing.

Lloyd’s List reported Grace 1 had “a complex ownership chain” and was controlled by Russian Titan Shipping, a subsidiary of TNC Gulf, a Dubai-based shipping company. Executives connected with both companies hold Iranian university and technical qualifications, or list their names in Farsi.