LONDON (AP) — 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 shows 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.”

“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 the 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.

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.

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.