Britain announced plans Monday to develop and deploy a Europe-led "maritime protection mission" to safeguard shipping in the vital Strait of Hormuz in light of Iran's seizure of a British-flagged tanker in the waterway last week.

Briefing Parliament on the budding crisis, Foreign Secretary Jeremy Hunt accused Iran of "an act of state piracy" that must be met with a co-ordinated international reaction.

May's official spokesperson, James Slack, said Iran has seized a ship under false and illegal pretences and it needs to release it and its crew immediately.

Iranian officials suggested the Stena Impero was seized and taken to an Iranian port in response to Britain's role in seizing an Iranian oil tanker two weeks earlier off the coast of Gibraltar, a British overseas territory on the southern tip of Spain.

Hunt announced precious few details of the proposed protection mission, but said Britain's European allies will play a major role in keeping shipping lanes open. One-fifth of all global crude exports passes through the narrow strait between Iran and Oman.

Also on Monday, Iran released new video showing the ship's crew for the first time, an apparent attempt to show they were unharmed. None of the 23 are British nationals but are mostly Indian and also Filipino, Russian and Latvian nationals.

U.K. tells Iran to back off

The foreign secretary said Iran must understand that its actions will only lead to a bigger Western military footprint in the region.

"It is with a heavy heart that we are announcing this increased international presence in the Gulf, because the focus of our diplomacy has been on de-escalating tensions in the hope that such changes would not be necessary," Hunt said.

This image taken from video aired by the Islamic Republic of Iran Broadcasting (IRIB) on Monday shows some of the 23 crew members of the British-flagged tanker Stena Impero. (IRIB News Agency via AP)

He also sought to put distance between Britain and its closest international ally, the United States.

Washington has broken with London on Iran policy as a result of President Donald Trump's rejection of the international accord designed to prevent Iran from developing nuclear weapons. Trump pulled the U.S. out of the accord last year and re-imposed harsh sanctions, which have had a severe effect on Iran's economy.

The foreign secretary said the planned European mission was not part of the U.S. policy of exerting "maximum pressure" on Iran.

It was unclear which countries will join the protection force or how quickly it can be put in place. Hunt said he had consulted with foreign ministers of Oman, the U.S., France, Germany, Italy, Finland, Spain and Denmark.

Iran's government spokesman Ali Rabiei said that there are diplomatic solutions to the current crisis, but he also defended Iran's actions.

"When you illegally seize a ship in Gibraltar … we don't deem it as necessary to show tolerance," he said. "Some countries have asked for the immediate release of the British tanker. Well, we ask those countries to make the same request to Britain first."

A picture taken on Saturday shows Iranian Revolutionary Guards patrolling around the British-flagged tanker Stena Impero as it's anchored off the Iranian port city of Bandar Abbas. (Hasan Shirvani/AFP/Getty Images)

Britain says it acted lawfully off the Gibraltar coast to prevent illegal oil shipments to Syria that would have violated European Union sanctions. It says Iran broke international maritime law by forcing the Stena Impero to change course and go to Iran.

However, Iran's Foreign Minister Mohammad Javad Zarif said the Stena Impero was in violation of "international law on safe passage" in the Strait of Hormuz on the day it was seized. Speaking Monday during a visit to Nicaragua, he said the British ship had "turned off its signalling" for longer than is allowed and "was passing through the wrong channels."

Britain also says the tanker was in Omani waters at the time, which Iran disputes.

Iran releases footage of seized tanker

In a newly released video on Monday, the Stena Impero crew is seen dressed in red uniforms and seated around a table onboard as an unidentified Iranian man is heard thanking them for their cooperation. A cameraman is heard telling them not to look at the camera.

Audio of U.K. warship warning Iran military against seizing tanker:

A recording has surfaced of radio messages between an Iranian military commander and a U.K. warship just minutes before the capture of a British tanker in the Persian Gulf. 1:26

It wasn't clear if the crew was under duress to take part in the filming.

Other choreographed shots show a man checking on the ship, the crew sharing a laugh and talking next to a coffee machine inside the ship. The crew's chefs are seen preparing food. Another video released by Iran's state broadcaster shows Iran's flag hoisted on the ship's bridge.

As the nuclear deal between Tehran and world powers unravels, the U.S. has expanded its military presence in the region, while Iran has begun openly exceeding the uranium enrichment levels set in the accord to try to pressure Europe into alleviating the pain caused by the sanctions.

European nations, which are trying to save the nuclear deal and keep Iran from isolation, have tried to come up with ways to keep trading with Iran but have run smack into Trump's sanctions, which also target Iranian oil exports.

Britain is adding to its military profile in the region but it does not have the naval resources that would be needed to protect all of its shipping interests. Scores of vessels pass through the Strait of Hormuz each day, where shipping lanes are just two miles wide at its narrowest. More than 400 transits through the passage were made last year by U.K. associated ships.

Iranians undeterred by officer's query

Also Sunday, an audio released by maritime security risk firm Dryad Global shows that a British frigate was too far away from the seized tanker to keep it from being diverted into an Iranian port, despite U.K. efforts to keep it from being boarded.

In the audio, a British naval officer from HMS Montrose patrolling the area around the Strait of Hormuz, which is at the mouth of the Persian Gulf, is heard telling the Iranian patrol boat: "Please confirm that you are not intending to violate international law by unlawfully attempting to board the MV Stena."

His words did nothing to deter the Iranians.

British officials say HMS Montrose was roughly 60 minutes from the scene when the Iranians took control of the tanker, too far away to intervene effectively as it had a week earlier when it warned off Iranian Guard vessels during an escort of a British commercial oil tanker.