Foreign Secretary Jeremy Hunt outlined plans to the British parliament after a meeting of the government's emergency committee, which discussed London's response to Friday's capture of the Stena Impero tanker by Iranian commandos at sea.

"Under international law, Iran had no right to obstruct the ship's passage - let alone board her. It was therefore an act of state piracy," Hunt told parliament.

"We will now seek to put together a European-led maritime protection mission to support safe passage of both crew and cargo in this vital region," Hunt said.

The British announcement signals a potential shift from Washington's major European allies who so far have been cool to US requests that they beef up their military presence in the Gulf, for fear of feeding the confrontation there.

It is unclear how much influence Britain may have in Europe given it is about to have a new prime minister, widely expected to be Boris Johnson, who takes over a country divided over Brexit, its planned departure from the European Union.

Hunt said the maritime protection proposal would not involve contributing European military power to back Washington's hardline stance against Iran.

The proposed new maritime protection mission "will not be part of the US maximum pressure policy on Iran because we remain committed to preserving the Iran nuclear agreement", he said.

In Nicaragua, Iranian Foreign Minister Mohammad Javad Zarif accused the British tanker of endangering shipping by turning off its signal for longer than permitted and by "passing through the wrong channel."

Zarif said Iran's actions were not in retaliation for the British capture of an Iranian tanker two weeks earlier in Gibraltar and he warned the West against "starting a conflict," saying Tehran was not seeking confrontation.

"Starting a conflict is easy, ending it would be impossible," Zarif told reporters after meeting his Nicaraguan counterpart.

"It's important for everybody to realise, it's important for Boris Johnson to understand, that Iran does not seek confrontation."

Washington's major European allies Britain, France and Germany all opposed US President Donald Trump decision last year to abandon an international agreement that gave Iran access to trade in return for accepting curbs on its nuclear programme.

The Europeans have tried to stay neutral as tensions have risen between Tehran and Washington.

But Britain was plunged directly into the crisis on July 4 when it seized an Iranian tanker off Gibraltar accused of violating sanctions on Syria.

Iran repeatedly threatened to retaliate, culminating with its seizure of the Stena Impero on Friday using the same tactics - commandos rappelling to the deck from helicopters - that British Royal Marines had used aboard Iran's own ship.

Almost a fifth of the oil consumed globally passes through the Strait of Hormuz.

Australian Associated Press