Britain has been plunged into a diplomatic row with Iran after Royal Marines seized an Iranian oil tanker as it passed through the Strait of Gibraltar, in a move likely to further inflame tensions in the Gulf.
The Grace 1 supertanker was boarded in the early hours of Thursday (Thursday afternoon NZ time) to prevent it from delivering a cargo of crude oil to Syria in defiance of EU sanctions, apparently following a request to the UK from the US.
The move provoked fury in Iran, which accused Britain of bowing to US pressure to blockade its oil exports and summoned the British ambassador to the foreign ministry in Tehran to express "its very strong objection to the illegal and unacceptable seizure" of the 1080-foot (329-metre) vessel.
Abbas Moussavi, a spokesman, called the move "destructive" and said it could increase tensions in the Persian Gulf, where six oil tankers have suffered attacks that Britain and the US have blamed on Iran.
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A specialist team from the Royal Marines' maritime operations unit swooped as the vessel paused to take on supplies off Gibraltar overnight.
The 30 commandos boarded the ship by abseiling from a Wildcat helicopter and climbing aboard from a Pacific 24 high-speed boat, allowing 16 Royal Gibraltar Police officers to search the vessel in a safe manner.
The operation was over in minutes with no shots fired. Fabian Picardo, Gibraltar's Chief Minister, said he authorised the assault because he believed the ship was bound for the Baniyas refinery in Syria.
​Josep Borrell, Spain's foreign minister, said Britain had acted at the request of the US. Borrell added that Madrid was assessing the implications of the incident because it took place in waters it considers its own.
Britain's Foreign Office said Rob Macaire, the UK ambassador in Tehran, told the foreign ministry that the move was about enforcing sanctions on Syria, not on Iran, and that Britain views Iranian oil exports in general as legitimate.
Lloyd's List, the shipping publication, said the 300,000-ton, Panamanian-flagged tanker loaded oil off Iran in April before sailing around the Cape of Good Hope, a lengthy route apparently taken because the ship was too heavy to use the Suez Canal.
The vessel was one of four found to be involved in shipping Iranian fuel oil in violation of US sanctions by a Reuters investigation earlier this year.
Its seizure will further inflame the difficult relationship between Britain and Tehran, which has clashed recently over the fate of jailed dual national Nazanin Zag