British Royal Marines in fast boats boarded a super tanker in an early-hours operation aimed at cutting suspected Iranian oil supplies to the regime of Syrian President Bashar Al Assad. Gibraltar’s government said it believed the MT Grace 1 was breaching European Union sanctions by shipping crude to the Baniyas Refinery in Syria, which is under the control of the regime. The seizure sparked fury in Tehran where the British ambassador was summoned to explain the “illegal interception” of the ship, according to Iran’s foreign ministry. The operation was described as the first of its kind to enforce European Union sanctions. Spain’s acting foreign minister, Josep Borrell, claimed that the UK was acting at the behest of the United States, which has taken an increasingly robust stance against Iran. It comes amid heightened tensions between Iran and the United States following attacks on tankers in the Straits of Hormuz, which the US has blamed on covert operations organised by Tehran. The US has sent warships and planes to the region to back up its threat amid fears of a wider conflict. The 30 British marines boarded from fast boats and a helicopter after a request from Gibraltar's chief minister to support the local police operation, the British defence ministry said on Thursday. The operation came less than two weeks after an attack on pipelines off Syria’s coast that are used to deliver crude oil from tankers to the Syrian refinery. The attack, which a Syrian official said was conducted with the help of an unidentified foreign state, reportedly disrupted an Iranian crude oil shipment. The government of Gibraltar, a British territory which sits at the entry point to the Mediterranean, detained the super tanker, a 300,000-tonne tanker under the Panama flag operated by a Singapore-based company, at about 2am on Thursday. “That refinery is the property of an entity that is subject to European Union sanctions against Syria,” said the territory's Chief Minister Fabian Picardo. “We have detained the vessel and its cargo.” Britain’s foreign secretary, Jeremy Hunt, welcomed the seizure saying it had “denied valuable resources to Assad’s murderous regime”. The Gibraltar authorities didn't confirm the origin of the ship's cargo but Lloyd's List, a publication that specialises in maritime affairs, reported this week that the Panama-flagged tanker was laden with Iranian oil. Data from financial technology specialists, Refinitiv Eikon, also indicated the ship sailed from Iran, and the cargo was Iranian crude. The mapping data showed the Grace 1 sailed a longer route around the southern tip of Africa instead of via Egypt's Suez Canal. The tanker was documented as loading fuel oil in Iraq in December, though the Iraqi port 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 Assaluyeh, fully loaded. Iran restarted crude oil deliveries to Syria in May in defiance of US sanctions, following a lull in shipments since the end of 2018. The US tightened the screw on Iranian oil exports – its main source of export income – after President Donald Trump withdrew from the 2015 nuclear deal and in May ended sanctions waivers for oil importers. European Union sanctions against Syria have been in force since late 2011 shortly after the start of the bloody crackdown against pro-democracy demonstrators. They targeted 277 Syrian officials including government ministers, and froze the assets of 72 entities. The EU also introduced an embargo on Syrian oil, investment relations and froze Syrian central bank assets within the EU. Government-controlled areas of Syria suffered from acute fuel shortages earlier this year. In May, Syria received its first foreign oil supplies from six months with two shipments, including one from Iran. A British Foreign Office spokesman said: “We welcome this firm action by the Gibraltarian authorities, acting to enforce the EU Syria sanctions regime.”