Russia’s communications watchdog says it has asked a court to block access to a popular messaging app.

The Russian Communications Agency said on Friday it has filed a lawsuit against the messaging app Telegram after it refused to hand over encryption keys to Russian intelligence.

The announcement follows a months-long row between Telegram and Russian authorities, who insist they need access to the keys to investigate serious crimes including terrorist attacks.

Russia’s Supreme Court last month threw out an appeal by Telegram against demands from the Federal Security Service intelligence agency to provide access to user data.

Telegram argues that the FSB violates consumer rights, while authorities say the app has been used by violent extremists.