Iran's Revolutionary Guard Corps (IRGC) have released footage showing a British oil tanker being seized in the Strait of Hormuz on Friday.
The Stena Impero tanker "was confiscated by the Revolutionary Guards at the request of Hormozgan Ports and Maritime Organisation when passing through the Strait of Hormuz, for failing to respect international maritime rules".
The video of the incident showed Iranian soldiers in black ski masks rappelling from a helicopter onto the vessel.
It also shows several small IRGC boats surrounding the larger tanker as it moves through the strait. A military helicopter hovers above and several men wearing black masks begin to rappel onto the ship.
The video was shot with at least two cameras, one from a speed boat-like vessel and one from the helicopter, which captured the men as they prepared to slide down a rope and also took aerial footage of the tanker.
The episode prompted condemnation from the UK and its European allies as they continue to call for a de-escalation of tensions in the critical waterway.
UK Foreign Secretary Jeremy Hunt said Britain's response "will be considered but robust".
In comments on Twitter on Saturday, Hunt said he spoke with his Iranian counterpart but was disappointed by Iran saying it wanted to de-escalate the situation but "have behaved in the opposite way".
"This has [to] be about actions not words if we are to find a way through. British shipping must & will be protected," said Hunt.
The free flow of traffic through the Strait of Hormuz is of international importance because one-fifth of all global crude exports passes through the waterway from Mideast exporters to countries around the world.
The narrow waterway sits between Iran and Oman.
The owner of Stena Impero, Stena Bulk, said the vessel was stopped by "unidentified small crafts and a helicopter" during its transit through the Strait of Hormuz.
It was seized with a crew of 23 crew aboard, although none are British nationals.
Hunt said the ship's seizure shows worrying signs Iran may be choosing a dangerous and destabilising path. He also defended the British-assisted seizure of Iran's supertanker two weeks ago as a "legal" move because the vessel was suspected of breaching European Union sanctions on oil shipments to Syria.
But Iran's Foreign Minister Mohammad Javad Zarif characterised the seizure of Iran's tanker July 4 as "piracy" in comments he made on Twitter, adding that the objective behind Iran's actions on Friday was to uphold international maritime rules.
Al Jazeera's Dorsa Jabbari, reporting from Tehran, said the IRGC spokesperson added there was a British warship that was accompanying the oil tanker.
"The warship did try to intervene and prevent the Guards from seizing this vessel," Jabbari said.
"The ship will go through the due legal procedures before it is going to be released … Iran was carrying out its due diligence in the waters of the Strait of Hormuz," she added, citing Iranian officials.
The move by Iran has drawn condemnation from European signatories to Iran's nuclear accord with world powers.
Germany and France both called on Iran to immediately release the ship and its crew, with Berlin saying the seizure undermines all efforts to find a way out of the current crisis.
Europe has struggled to contain the tensions that stem from US President Donald Trump's decision to pull the US from Iran's nuclear deal, which had lifted sanctions on Iran in exchange for compliance on its nuclear program.
Trump has since re-imposed sweeping sanctions on Iran, including its oil exports, and Iran recently increased uranium enrichment levels beyond limits of the deal in a bid to pressure Europe into finding a workaround the crippling economic sanctions.
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