The release Sunday of an audio recording has shed new light on the seizure of a British-flagged tanker at the hands of Iran's Revolutionary Guard as tensions flare in the strategic Strait of Hormuz.

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

On the recording, a stern-voiced British naval officer insists that the U.K.-flagged oil tanker Stena Impero must be allowed to sail through the Strait of Hormuz even as Iranian paramilitary forces demand — successfully — that the vessel change course.

The audio shows how Britain's once-mighty Royal Navy was unable to prevent the ship's seizure, which has been condemned by Britain and its European allies as they continue to call for a reduction of tensions in the vital waterway.

The free flow of traffic through the Strait of Hormuz is of critical importance to the world's energy supplies because one-fifth of all global crude exports pass through the narrow waterway between Iran and Oman.

In the recording, an Iranian officer can be heard telling the Stena Impero to change course, saying: "You obey, you will be safe."

Audio of U.K. warship warns 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

"Alter your course to 360 degrees immediately, over," the Iranian officer says, adding that the ship is wanted for security reasons.

A British naval officer from HMS Montrose frigate that was patrolling the area around the Strait of Hormuz is heard telling the Stena Impero, which had a crew of 23 on board, that its passage must be allowed.

"Sir, I reiterate that as you are conducting transit passage in a recognized international strait, under international law your passage must not be impaired, intruded, obstructed or hampered," the unidentified British officer says.

The British officer then tells an 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 the HMS Montrose was roughly 60 minutes from the scene when the Iranians took control of the tanker, too far away to intervene effectively.

Iranian officials say the seizure of the British oil tanker was a justified response to Britain's role in impounding an Iranian supertanker two weeks earlier off the coast of Gibraltar, a British overseas territory located on the southern tip of Spain.

'This is about preventing war'

Friday's seizure comes amid heightened tensions between the U.S. and Iran stemming from President Donald Trump's decision last year to pull the U.S. from Iran's nuclear accord with world powers and reinstate sweeping sanctions. The U.S. has also expanded its military presence in the region, while Iran has begun openly exceeding the uranium enrichment levels set in the nuclear 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

British Foreign Secretary Jeremy Hunt says the government plans to spell out its response in a briefing to Parliament on Monday. Officials have said a military response is extremely unlikely and Britain has taken steps to bolster its diplomatic efforts.

U.K. Foreign Secretary Jeremy Hunt leaves a meeting at 10 Downing Street for talks about the captured oil tanker on Saturday. (Aaron Chown/PA via AP)

The tanker seizure comes at a ticklish time for Britain, which on Wednesday will see a new prime minister replace Theresa May. The two contenders for the job are front-runner Boris Johnson and Hunt, who has a key role in dealing with the shipping crisis.

British officials say they have no good military options, especially because the tanker is in a secure Iranian port with a heavy military presence. Defence minister Tobias Ellwood on Sunday reiterated calls for a tamping down of tensions.

"Well, firstly we need to try and de-escalate this," he told Sky News. "There has been a ratcheting up of tensions in the Middle East."

Ellwood called the seizure "a hostile act" but conceded that the British Royal Navy "is too small to manage our interests across the globe" and that this would be an issue for the next prime minister to handle.

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.

The seizure of the British-flagged tanker is proving popular inside Iran.

In Tehran, some 160 lawmakers issued a joint statement Sunday praising the interception of the British-flagged vessel by Iran's Revolutionary Guard, which has released video of the seizure showing Iranian commandos in black ski masks and fatigues rappelling from a helicopter onto the vessel.

Iran's Foreign Minister Mohammad Javad Zarif used the opening session of the Non-Aligned Movement (NAM) forum in Venezuela on Saturday to blast U.S. foreign policy under Trump.

Iranian Foreign Minister Mohammad Javad Zarif is seen at the United Nations headquarters on Thursday. (Frank Franklin II/Associated Press)

"A new wave of extreme one-sided adventurism from the United States is the main theme and the challenge that we all face in one way or another," he said. "It's threatening peace and stability all around the world in different ways."

At the same time, Britain is gaining support among its traditional European allies. Germany's foreign minister warned Iran that its seizure of commercial vessels is contributing to an "escalation spiral" that could lead to war.

Foreign Minister Heiko Maas was quoted Sunday in the Bild newspaper as saying the seizure of the British tanker and the temporary detention of another has made the situation in the Gulf "a lot more serious and dangerous than it has been." He said European efforts are focused on keeping diplomatic channels open with "voices of reason" despite the challenges involved.

"This is about preventing war," he said.