"The terrorists' activities have been coordinated through the Telegram app," a statement, issued by the service says.
The terrorists planned to conduct terrorist acts in Moscow. The FSB further noted that is also managed to define the terrorists' supporters in the city.
Last week, Russia's Internet watchdog Roskomnadzor began blocking the Telegram messenger in Russia in accordance with a court decision.
According to the security service, the messenger is often being used by terrorists to coordinate terror attacks on Russian soil.