Footage showing the moment Iran's Revolutionary Guard seized a British-flagged oil tanker in the Strait of Hormuz has been released - with the UK describing the incident as a "hostile act".

The video, released by Iranian state media, shows armed troops wearing ski masks sitting in a helicopter as it hovers above the Stena Impero. Several of them are then seen rappelling onto the ship's deck as speedboats surround the oil tanker.

Defence Secretary Penny Mordaunt said the Stena Impero, which was not carrying cargo, had been in Omani waters when it was stopped by the Iranian Revolutionary Guard on Friday afternoon.

Image: Footage released by Iran shows armed troops rappelling onto the ship from a helicopter

Latest developments:

Foreign Secretary Jeremy Hunt has told his Iranian counterpart he is "extremely concerned" by the seizure. He also warned there will be "serious consequences" if the tanker is not released

UK government's emergency Cobra meeting discussed guaranteeing security of shipping

The UK's Foreign Office has summoned Iran's charge d'affaires

Stena Bulk, which operates Stena Impero, is making a formal request to visit the vessel. The company has been told its crew members are in "good health"

The Iran Revolutionary Guard said it managed to bring the Stena Impero to Iranian shores despite "resistance and interference" from a British warship

But Defence Secretary Penny Mordaunt told Sky News that HMS Montrose was 60 minutes away from being able to help

Iranian authorities have said crew members may be interviewed by authorities on "technical matters"

Labour leader Jeremy Corbyn has called for the British-flagged tanker and its crew to be released - but said all sides must show restraint as escalation risks a "deeper conflict"

France said it is "very concerned" by the seizure, and Germany described it as an "unjustifiable intrusion"

The European Union has warned the development "brings risks of further escalation"

Following the UK's emergency Cobra meeting, Foreign Secretary Jeremy Hunt stressed that he wants a diplomatic solution to the incident.

Hunt warning as UK-flagged vessel captured

Tehran had initially said the tanker was detained because it had collided with an Iranian fishing boat.


But on Saturday, the country directly linked the seizure of the tanker to Britain's role in detaining a tanker carrying Iranian oil earlier this month.

A spokesman for Iran's Guardian Council was quoted as saying that "the rule of reciprocal action is well-known in international law" - and that Tehran made the right decision in face of an "illegitimate economic war and seizure of oil tankers".

Following Saturday's Cobra meeting, Mr Hunt said: "I had a fairly long conversation with the Iranian foreign minister. And it's clear from talking to him and also statements made by Iran that they see this as a tit-for-tat situation, following Grace 1 being detained in Gibraltar. Nothing could be further from the truth."

He said Grace 1 was detained legally in Gibraltarian waters because it was carrying oil to Syria in contravention of EU sanctions, while the Stena Impero was seized "in clear convention of international law".

Mr Hunt added: "It was then forced to sail into Iran. This is totally and utterly unacceptable. It raises very serious questions about the security of British shipping and indeed international shipping in the Straits of Hormuz."

Defence Sec: 'This was a hostile act'

During Friday's incident, a second oil tanker, the Liberian-flagged Mesdar, veered off course towards the Iranian coast after it was boarded by armed guards at about 5.30pm on Friday.

The Mesdar's Glasgow-based operator said communication had since been re-established with the ship and the crew were unharmed. The tanker was reportedly allowed to resume navigation.

Image: The Stena Impero is being held by Iranian authorities. File pic: Stena Bulk

Downing Street said Prime Minister Theresa May was in her constituency but was being kept informed of developments.

In a statement, Stena Bulk said ship manager Northern Marine Management had lost contact with the crew of 23 after "unidentified small crafts and a helicopter" approached the vessel on Friday afternoon.

Footage released by Iran's Revolutionary Guards has shown speedboats pulling up alongside Stena Impero - with troops wearing ski masks and carrying machine guns rappelling to its deck from a helicopter.

Erik Hanell, president and chief executive of Stena Bulk, said: "There are 23 seafarers onboard of Indian, Russian, Latvian and Filipino nationality.

"There have been no reported injuries and the safety and welfare of our crew remains our primary focus. We are in close contact with both the UK and Swedish government authorities to resolve this situation and we are liaising closely with our seafarers' families."

Image: The tanker's owner said the vessel was in international waters

Bob Seely, an MP and member of the foreign affairs committee, told Sky News that the situation with Iran in the Strait of Hormuz is "a massive crisis and it's going to get bigger".

He added: "The Iranians want to internationalise this crisis as much as possible.

"Their economy is hurting and what they want to do in order to get resolution is to widen this as much as possible. The only long-term solution is a Iranian nuclear deal that gets the US back in it. Until then we'll have a series of crises until a really big one blows up."

Sir Richard Dalton, former British ambassador to Iran, told Sky News: "The US needs to devise a serious policy for negotiating with Iran rather than insisting Iran surrender to an ever lengthening list of requirements."

Defence Sec: 'This was a hostile act'

The Iranian tanker Grace 1 was seized on 4 July off the coast of Gibraltar, accused of trying to take oil to Syria in violation of European Union sanctions.

Iran's supreme leader Ayatollah Ali Khamenei called the tanker's seizure an act of "piracy" and warned the UK to expect a response.

Just days later the Royal Navy frigate HMS Montrose, on patrol in the region, deterred Iranian patrol boats attempting to impede a British tanker sailing through the Strait of Hormuz, leading the government to deploy a second vessel, HMS Duncan, to the region.

British commercial ships have been warned to avoid the area.