Iran may be choosing a “dangerous path of illegal and destabilising behaviour” after its authorities seized a British-flagged tanker in the Strait of Hormuz, the foreign secretary has warned.

The Islamic Revolutionary Guard took control of the UK-registered Stena Impero over what it claimed were violations of international maritime rules at around 4pm UK time on Friday.

The capture comes just weeks after British royal marines took control of Iran’s Grace 1 tanker in Gibraltar on July 4 on suspicion of transporting fuel to Syria.

A second British-owned oil tanker, the Liberian-flagged MV Mesdar, was also boarded by armed guards shortly afterwards and was seen to veer some distance off-course towards the Iranian coast.

Around five hours after it changed direction, the vessel’s Glasgow-based operator said communication had since been re-established with the ship and the crew were unharmed.

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Defence sources told The Independent there was surprise in Westminster at the seizures, given the UK’s recent offer to release the Grace 1 if Iran could guarantee it would not travel to Syria.

The UK government has said it is “deeply concerned” about Iran’s “unacceptable actions” and it has advised UK vessels to stay out of the area for an interim period.

On Saturday, British foreign secretary Jeremy Hunt tweeted: “Yesterday’s action in Gulf shows worrying signs Iran may be choosing a dangerous path of illegal and destabilising behaviour after Gibraltar’s legal detention of oil bound for Syria.

“As I said yesterday our reaction will be considered but robust. We have been trying to find a way to resolve Grace 1 issue but will ensure the safety of our shipping.”

The Revolutionary Guards also denied they had captured the tanker, Iran’s semi-official Tasnim news agency reported, quoting regional military sources. The report said it “was allowed to continue its course after being warned about safety issues by Iranian forces.”

Stena Bulk, the owners of the Stena Impero, said it was “was approached by unidentified small crafts and a helicopter during transit of the Strait, while the vessel was in international waters” at 4pm.

The Stena Impero is seen to stop in its tracks before turning towards Iran (Marinetraffic.com)

There were 23 crew members aboard, the company said in a statement, adding that there were Indian, Russian, Latvian and Filipino in nationality. The ship “is no longer under the control of the crew and remains uncontactable”, the spokesman added.

The official spokesperson for the Indian government said: “We are ascertaining further details on the incident. Our Mission is in touch with the Government of Iran to secure the early release and repatriation of Indian nationals.”

A port authority chief was quoted by Tasnim, which is closely affiliated with the Revolutionary Guard, as saying: “We received some reports on the British oil tanker, Stena Impero, causing problems, and therefore we asked the military forces to guide this tanker towards Bandar Abbas harbour to have the required investigations carried out.”

Unnamed sources were also saying the tanker had been causing pollution by dumping oil residue.

The Government’s emergency committee Cobra met on Friday night to discuss the situation.

“We remain deeply concerned about Iran’s unacceptable actions which represent a clear challenge to international freedom of navigation,” a Government spokesman said.

The spokesman added: “As the Foreign Secretary has said, our response will be considered and robust and there will be serious consequences if the situation is not resolved.”

Sources added that the destroyer HMS Duncan, currently sailing to relieve the HMS Montrose in the Gulf region, may well now operate alongside the frigate. The Montrose faced down Revolutionary Guard gunboats as they tried to impede the progress of a BP oil tanker through the Strait last week.

After the ministers met for an emergency Cobra committee, a government spokeswoman said they were “deeply concerned about Iran’s unacceptable actions which represent a clear challenge to international freedom of navigation.

“We have advised UK shipping to stay out of the area for an interim period.”

US president Donald Trump said he would consult with Britain about the incident, following a verbal battle with Tehran earlier in the day over whether a US navy ship had indeed brought down an Iranian drone in the Strait this week, which Tehran denies.

Bob Sanguinetti, of the UK Chamber of Shipping, condemned the Revolutionary Guard’s move. He said: “The action by those involved is in violation of international regulations. This incident represents an escalation.

“Whilst we call for measured response, it is also clear that further protection for merchant vessels must be forthcoming to ensure enhanced security to guarantee free flow of trade in the region.”

The seizure of ships comes after weeks of rising tensions not just over Grace 1 being sequestered, but Iran’s restarting of uranium enrichment in protest at tough US sanctions.

After Mr Trump unilaterally withdrew the US from a long term nuclear agreement it had signed with five other world powers including the UK, tensions have worsened.

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Iran has refused to negotiate any changes, and has threatened to further break the terms of the agreement if Europe does not help limit the effects of US sanctions. It has also broken restrictions on its production of enriched uranium, used to make reactor fuel but also potentially nuclear bombs.

European leaders want to maintain the agreement but have not been able to address Iranian demands, particularly concerning the sale of oil, without violating the sanctions.

The Stena Impero’s seizure marked a “more significant escalation”, according to Vikram Singh, a former deputy assistant defence secretary under Barack Obama.

He told Sky News: “Even more than with the drama of the downing of drones … this starts to seem like a really major threat to the transit of oil and energy supplies.”

The incident could push European powers closer to the US on Iran policy following the schism over Mr Trump’s withdrawal from the nuclear agreement, Mr Singh added.

Labour shadow chancellor John McDonnell said the seizure of a British oil tanker was “unacceptable” and called for it to be released.

He said: “The Iranian government is obviously to blame for taking the tanker, it’s unacceptable behaviour and we echo what the Government has said.