MOSCOW, June 26. /TASS/. Russia's intelligence service FSB fixes total use by members of secret terrorist groups of messengers, and most actively they use the Telegram messenger, the service's PR Department told TASS on Monday.

"The Federal Service for Security (FSB) during the searches to reveal secret groups of international terrorist organizations fixes a total use by their members of the Internet-based messengers in their secret communication between themselves and with the foreign curators," FSB said.

"Most actively, members of international terrorist organizations in the territory of the Russian Federation are using the Telegram messenger, which allows the terrorists having chats with a high level of encrypted information," the service said.

The Telegram messenger was used by the terrorist and plotter of the terrorist attack in St. Petersburg's metro on April 3, FSB added. "During the investigation into the terrorist attack of April 3 in St. Petersburg's metro, FSB received reliable information that the suicide bomber, his allies and the foreign curator used the Telegram messenger for concealing their criminal plots at all the stages of preparations for the terrorist attack," FSB said.