Masked Iranian troops are seen abseiling onto a tanker in new footage that appears to show the moment the British vessel held by Tehran was captured.
In the clip, released by Iran, a helicopter flies over the vessel before commandos on board lower themselves down by rope.
The tanker, with 23 crew, had suddenly veered off course, heading into Iranian waters in the Strait of Hormuz.
The footage, from Tehran’s Revolutionary Guard-affiliated Fars news agency, appears to reveal how the tanker was followed by high-speed boats and combat troops.
Iran claimed it took control of the vessel because it had collided with an Iranian fishing boat, but Penny Mordaunt, the defence secretary, said this was untrue.
Instead, the tanker was intercepted inside Oman’s territorial waters, making Iran’s actions a “hostile act”, she said.
Jeremy Hunt, the foreign secretary, said Tehran saw the situation as a “tit for tat” for the detention of Iranian vessel Grace 1 in Gibraltar on earlier this month on suspicion of transporting fuel to Syria, against EU sanctions.
The Foreign Office summoned the Iranian chargé d’affaires to deal with the situation as Tehran ignored pleas by Britain, France and Germany to release the vessel.
A UK warship, the HMS Montrose, had sped to help the British tanker but arrived too late.
Sweden’s Stena Bulk, the owner of the Stena Impero, said the crew members, who are Indian, Russian, Latvian and Filipino, were in good health.
A second British-owned Liberian-flagged tanker, the MV Mesdar, was also boarded by armed guards around the same time but was released.
In increasingly aggressive action in the Gulf, Tehran has also targeted US ships, and last month the Revolutionary Guards shot down a US drone.
After Donald Trump unilaterally withdrew the US from the West’s nuclear agreement with Iran, tensions have deepened between the US and Tehran.
Iran has threatened to further break the terms of the agreement if Europe does not help limit the effects of US sanctions.
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