– A British warship tried but failed to prevent Iran’s Islamic Revolutionary Guard from seizing a British tanker in the Strait of Hormuz last week, intercepted radio communications show, fueling a wave of recriminations in London on Sunday over who was to blame.

In recordings obtained by the shipping consultancy Dryad Global and posted on its website Sunday, a member of the Revolutionary Guard is heard ordering the British-flagged Stena Impero tanker to divert course toward Iran. “Alter your course,” the man says. “If you obey, you will be safe.”

A British naval officer interrupts, telling the Stena Impero that it has the right to proceed. “Under international law your passage must not be impeded, obstructed or hampered,” he says. The British officer then addresses the Iranian: “Please confirm that you are not intending to violate international law by unlawfully attempting to board the MV Stena.”

He spoke from the British frigate HMS Montrose, one of two warships sent to the Persian Gulf to protect British shipping after Iran threatened to seize a British tanker in retaliation for Britain’s detention of an Iranian tanker in the Mediterranean earlier this month.

Neither Britain nor Iran challenged the authenticity of the recordings. Iran says it detained the Stena Impero for unspecified “violations” of maritime law.

A former head of the Royal Navy said the tanker should have been better protected before it was intercepted on Friday. In London, British Defense Minister Tobias Ellwood pushed the criticism aside. The priority now, Ellwood said, must be to “de-escalate tensions” with ­Tehran.

Asked whether Britain took its “eye off the ball” and failed to defend ships in crucial waterways, he replied: “No, not at all.” Soon after the exchange was recorded, Iranian commandos wearing balaclavas brazenly descended from a helicopter by rope onto the deck of the tanker, as Iranian fastboats closed in by sea, video posted by Iranian media shows.

On Sunday, Iran’s Press TV showed footage of the Stena Impero flying an Iranian flag. There was no sign of its 23-member crew, most of whom are Indian nationals. Iranian officials said the crew is safe.

Iranian Foreign Minister Mohammed Javad Zarif warned Britain not to escalate the situation. He accused U.S. National Security Adviser John Bolton of seeking to drag Britain “into a quagmire.”