"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.
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The decision to block the Telegram messenger app was made by the Roskomnadzor earlier in April after the company failed to give the Russian Federal Security Service (FSB) access to encryption keys in order to decipher messages, as required by Russian law. Telegram explained that it was impossible for them to provide the keys as the key to each specific chat is stored on users' devices.
According to the security service, the messenger is often being used by terrorists to coordinate terror attacks on Russian soil.