The messaging app, which has over 100 millions users worldwide, was used to plot a suicide bombing that killed 16, Russia's FSB security service said.
Russia could soon block Telegram, a messaging app used by 6 million in the country and over 100 million around the world.
Terrorists had used Telegram to plot a deadly suicide bombing in Saint Petersburg that left 16 dead, Russia's FSB security service said in a statement on Monday, adding it had "reliable information" on the matter.
The revelation came after Russian communications regulator Roskomnadzor issued Telegram a warning on Friday, saying it will ban the messaging app if it continues to refuse to "fill in a questionnaire" about its managing company so it can be registered as an "organiser of information dissemination" in the country.
In the statement, the FSB added that Telegram provided terrorists with a platform to "establish secret chat rooms with a high degree of encryption ."
Governments around the world have been pushing for social media companies to put more effort into combating terrorism. On Monday, ahead of the Five Eyes summit, Australia urged companies to "thwart" communication among terrorists, especially by weakening encryption. UK British Home Secretary Amber Rudd had previously called for WhatsApp to cooperate with intelligence agencies by allowing them access to encrypted texts following the Westminster attack in March.
Telegram was contacted for comment but did not immediately respond.
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