Russia has opened a criminal investigation into Pavel Durov, founder of Telegram, on suspicion of abetting terrorist activities, escalating tensions between the Kremlin and the messaging platform.

State media said the case was launched based on materials from Russia’s federal security service, which claims Telegram has been used in alleged Ukrainian-linked plots and refuses to cooperate with authorities.

Durov, who lives abroad and also founded VK, condemned the move as an attack on privacy and free speech.

Moscow has slowed Telegram’s traffic as part of its push for a state-controlled alternative and a more tightly regulated “sovereign internet,” though it has stopped short of banning the app due to its widespread use, The Guardian has reported.

The investigation marks the latest chapter in Durov’s long-running and complicated relationship with the Russian government, which previously attempted to block Telegram in 2018.