Russia's state communications watchdog, Roskomnadzor, has filed a lawsuit to block Telegram in the country because the instant messaging company has refused to hand over the encryption keys that would allow Russian authorities to read messages sent using the service. From a report: Ranked as the world's ninth most popular mobile messaging app, Telegram is widely used in countries across the former Soviet Union and Middle East. Active users of the app reached 200 million in March. As part of its services, Telegram allows users to communicate via encrypted messages which cannot be read by third parties, including government authorities. But Russia's FSB Federal Security service has said it needs access to some messages for its work, including guarding against terrorist attacks. Telegram has refused to comply with its demands, citing respect for user privacy.