In a post on the Telegram messaging app, bihus.info, which regularly publishes investigative stories about officials and wealthy private individuals, said an SBU unit had 30 people spying on its journalists during a corporate event at a hotel in December.

“Who represents the greatest threat to national security in wartime?” bihus.info said on Telegram. “Clearly journalists, in the opinion of the SBU.”

The SBU responded by saying in a statement it upheld the principles of a free press as part of its mission to defend national interests and a criminal investigation was launched into the use of spy technology.

A source within the organisation told reporters that the head of one of its units, the national statehood defence department, was dismissed after the allegations were made public last month.

In a statement on Telegram, the SBU said some members of the media outlet were identified as customers of drug dealers.

Last month, a video posted online by a little known group showed bihus.info members at the December event using recreational drugs and talking about procuring cannabis and MDMA, which are illegal in Ukraine. Bihus.info acknowledged the video was genuine, condemning both the use of drugs and the surveillance of its employees.

Ukrainian president Volodymyr Zelensky announced an investigation into the surveillance and denounced attempts to pressure journalists.