Russia’s state communications watchdog Roskomnadzor said on Friday it had filed a lawsuit in a Moscow court asking it to block Telegram messaging app, the BBC reports.
The move comes after the firm refused to hand over encryption keys used to scramble messages. Telegram was given a deadline of 4 April to hand over the keys.
Russia's main security agency, the FSB, wants the keys so it can read messages and prevent future terror attacks in the country.
Telegram's lawyer, Pavel Chikov, said the official attempt to stop the app being used in Russia was "groundless".
"The FSB's requirements to provide access to private conversations of users are unconstitutional, baseless, which cannot be fulfilled technically and legally," he said in a statement.
Russian presidential spokesman Dmitry Peskov described the app as “a convenient tool to communicate with journalists” and said “it will be a pity if no consensus is reached, TASSews agency said.
Telegram insists it cannot comply with this demand because it employs end-to-end encryption.
Last month creator Pavel Durov said it would not "give up" the private data of its users.
"Telegram will stand for freedom and privacy," he said in a Tweet post.
Threats to block Telegram unless it gives up private data of its users won't bear fruit. Telegram will stand for freedom and privacy.
— Pavel Durov (@durov) March 20, 2018
Telegram is also currently trying to raise funds for expansion via an ICO. This involves investors buying into a crypto-currency, called Gram, created and run by the firm. So far, it is believed to have raised about $1.7bn via this funding scheme.
By Siranush Ghazanchyan