Now, the FSB says that Akbarzhon Jailov, the terrorist that blew himself up in the St Petersburg metro on April 3, used Telegram to coordinate the attack and communicate with "his accomplices and their mastermind overseas to hide their criminal plots at all the stages of preparation for the terrorist attack."According to Durov, the agency requested the encryption keys, so it can read users' correspondence and catch other terrorists before they manage to pull off their plans".
It follows concern expressed by United Kingdom and European experts over a platform that has been dubbed the communications tool of choice for Islamic State.
Russia's FSB security agency today said the Telegram messaging service was used by those behind the Saint Petersburg metro bombing, the latest salvo by authorities after they threatened to block the app.
When Peskov was asked to comment on the words of the Telegram founder Pavel Durov that lock messenger is contrary to the Constitution, a spokesman said curtly: "This is not our issue".
The FSB's revelation made no mention of a threat on Friday by Russia's communications regulator Roskomnadzor to block the app over its failure to register Telegram as a disseminator of information in Russian Federation.More news: Recreational boat with 150 aboard sinks near Colombian city
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Telegram has been used by jihadists in France and the Middle East too, although the app company has highlighted its efforts to close down pro-IS channels.
"However, as soon as Telegram is blocked, all correspondence between Russian officials and their friends and families and other sensitive data in WhatsApp/Viber would be passed to US-controlled Apple iCloud/Google Drive", Durov said in a statement posted on Russia's Vkontakte social network, which he also founded. If Russia banned Telegram, he said terrorists would simply switch to Telegram's many competitors which also offered end-to-end encryption.
"During the operational participation in the investigation into the terrorist attack in St. Petersburg underground on April 3, the FSB has obtained credible information that the suicide bomber, his fellows and a foreign supervisor had used Telegram messenger to hide their criminal plot at all stages of the preparation for the terrorist attack", the FSB statement said.
Three flagship news shows on Russian state television featured reports on Telegram.
"To defeat terrorism through blocking, one must block the internet", Durov concluded.