IRAN today summoned the British ambassador in Tehran for heated diplomatic talks after Royal Marines stormed a Syria-bound supertanker over fears it was violating EU oil sanctions.
Troops in a military chopper from 42 Commando - backed by comrades in a speedboat - led the dramatic operation in Gibraltar's waters during the early hours of this morning.
However, Iran has now hit out at what it calls the "illegal seizure" of the ship and its contents.
A foreign ministry spokesman told Iranian TV the seizure was "destructive" and could increase tensions in the Gulf.
The 30 marines in a Wildcat helicopter were flown out to lead the mission at the request of the Gibraltar police - before abseiling onto the deck of the "rogue" tanker.
UK Ministry of Defence sources said that British troops were at all times acting under civil authority, at the direction of the Gibraltar police.
The marines provided the technical expertise to allow the vessel to be boarded at sea.
The Panama-flagged vessel - reportedly carrying Iranian crude oil - was boarded in the early hours by local cops and customs agents aided by the marines detachment.
It was boarded while carrying out an off-port-limits logistics stop in British territorial waters, where it had been due to collect food and goods while transiting past the Rock.
"We have reason to believe that the 'Grace 1' was carrying its shipment of crude oil to the Baniyas Refinery in Syria," said the British territory's Chief Minister Fabian Picardo.
"That refinery is the property of an entity that is subject to European Union sanctions against Syria. We have detained the vessel and its cargo."
Mr Picardo also praised the bravery of all those who detained the ship - which was closing in on its apparent destination when stopped.
"I want to thank the brave men and women of the Royal Marines, the Royal Gibraltar Police, HM Customs Gibraltar and the Gibraltar Port Authority for their work in securing the detention of this vessel and its cargo," he said.
"Be assured that Gibraltar remains safe, secure and committed to the international, rules-based, legal order."
It's believed the massive ship - which is more than 330m in length - left the Kharg Island oil terminal in Iran in mid-April.
The tanker then reappeared near the Iranian port of Bandar Assaluyeh fully loaded.
Why is Syria so desperate for oil?
War-torn Syria is in the grip of a massive oil crisis fuelled by crippling sanctions imposed by both the US and EU.
Years of conflict have drained its resources and it now needs to procure more than 75 per cent of its fuel from overseas.
With the strict sanctions in place, Damascus desperately needs to regain control of its oil fields in the east.
However, at the moment they are in the hands of the heavily-armed US-backed Syrian Democratic Forces.
Domestic oil production in 2018 reached 24,000 barrels a day - 20 per cent of its needs - down from 350,000 a day before the war.
Government officials say they now need £2.2 billion worth of subsidised fuel every year.
Iran, which offered vital military support to Bashar Assad, was the main provider.
However, the credit line Iran extended since 2013 to supply oil has run dry and its oil shipments seemingly stopped late last year.
This followed US sanctions imposed on a network that spanned Syria, Iran and Russia which was responsible for shipping oil to Assad's government.
After anchoring off the United Arab Emirates coast, the vessel headed 15,000 miles around Africa towards the Mediterranean.
Today's seizure comes just two weeks after Iran was accused of attacking tankers in the Gulf of Oman - an incident which almost triggered a war between the US and the Islamic Republic.
The two ships - Japan’s Kokuka Courageous and Norwegian-owned vessel the Front Altair - are now docked at the Emirati port of Fujairah.
Tehran has fiercely denied any involvement in the twin attacks on the pair of tankers.
TANKER ATTACKS
However, America blamed the Iranian Revolutionary Guard for planting limpet mines on the hulls of both vessels.
After this morning's operation, Mr Picardo said he has now written to the presidents of the European Commission and European Council to give details of the sanctions that have been enforced.
The EU has imposed a series of sanctions against Bashar Assad's regime in Syria in response to the conflict in the country.
The Syrian Sanctions Regime, established in May 2011, comprises financial, trade and transport restrictions.
The bloc imposed sanctions on 277 Syrian officials including government ministers over their role in the "violent repression" of civilians.
It has also introduced an embargo on Syrian oil and a strict freeze on Syrian bank assets within the EU.
The Foreign Office said this morning: "We welcome this firm action by the Gibraltarian authorities, acting to enforce the EU Syria Sanctions regime."