A German military officer used an unsecured phone line at a Singapore hotel to join a conference call that was hacked by Russians and leaked to the public, Germany’s defence minister said Tuesday.

The fallout from the leaked audio tape, which features four high-ranking German air force officers discussing hypothetically how Taurus long-range cruise missiles could be used by Kyiv against invading Russian forces, has embarrassed the German government and further increased tensions between the two countries.

“Not all participants adhered to the secure dialling procedure as intended,” German defence minister Boris Pistorius said as he briefed reporters in Berlin on the initial results of an ongoing investigation.

The minister said that the officer in question, whose name he did not give, had participated in the Singapore Air Show, which was attended by high-ranking military officers from across Europe.

He then dialled into the WebEx call using either his mobile phone or the hotel’s Wi-Fi but not a secured line as is considered mandatory for such calls.

“For the Russian secret services, it was a real find… targeted hacking took place in the hotels used across the board,” Mr Pistorius said.

“It must therefore be assumed that the access to this (phone) conference was a chance hit as part of a broad, scattered approach.”

Mr Pistorius said the investigation was ongoing, overall security had been increased and preliminary disciplinary proceedings were being considered, but that severe personal consequences were unlikely.

“I will not sacrifice any of my best officers to Putin’s games, to put it very clearly,” he said, referring to Russian President Vladimir Putin.

The 38-minute audio leak was posted by Margarita Simonyan, chief editor of the Russian state-funded television channel RT, on social media on Friday, the same day that Russian opposition leader Alexei Navalny was laid to rest after his still-unexplained death two weeks ago in an Arctic penal colony.

The recording also surfaced just weeks before Russia’s presidential election.

While German authorities have not questioned the authenticity of the recording, chancellor Olaf Scholz said last week that delivering those weapons to Ukraine was not an option — and that he does not want Germany to be drawn into the war directly.

However, on Monday Russia’s Foreign Ministry threatened Germany with “dire consequences” in connection with the leak. It did not elaborate.

Relations between the two countries have steadily eroded since Russia invaded Ukraine two years ago.