Earlier this week, another Telegram lawyer, Dmitry Dinze, told reporters that the company had notified Roskomnadzor that the FSB's requirement was not feasible for technical reasons, however, Roskomnadzor said in a press release that they had not received any official response from Telegram.
Telegram is the latest social platform to be targeted as the Russian government seeks to exert greater control over online communications. Facebook rejected similar demands.
Roskomnadzor said Telegram had 15 days to comply with its demands.
If Russia moves ahead with the ban, then domestic ISPs will have to blacklist domains and IP addresses that Telegram uses.
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Telegram agreed to do so, but it refused to provide encryption keys, which could disclose users' private data.
Telegram, which lets people exchange messages, photos, and videos in groups of up to 5,000 people, has attracted more than 100 million users since it was launched by a Russian Internet entrepreneur and his brother in 2013. Earlier, on March 20, Alla Nazarova, the judge of the Supreme Court of Russian Federation, dismissed the claim of the Telegram lawyers for cancellation of the FSB order regarding the decryption. "Telegram will stand for freedom and privacy", Durov wrote on Twitter at the time.
Telegram is now listed as the ninth most popular messaging app worldwide, roughly 200 million users, using software which it claims is more secure than mass market applications such as WhatsApp and Line.
While this will certainly be of interest to users in the country and worldwide, investors will also be watching closely as Telegram is also undertaking the world's biggest initial coin offering, with pre-sales reaching £1.7 billion already.