Russia's state media regulator has asked a court to block the messaging app Telegram following the company's refusal to give the Federal Security Service (FSB) access to users' messaging data.
In a statement on its website, Roskomnadzor said it had filed suit with Moscow's Taganka district court on April 6 seeking "restrictions on access to...Telegram on the territory of Russia."
The move may fuel concerns that Russia is seeking to curtail Internet freedoms following President Vladimir Putin's March 18 election to a new six-year term.
Shortly after Roskomnadzor issued the statement, Telegram lawyer Ramil Akhmetgaliyev said that the company did not plan to follow the order, dismissing the FSB's demand as "unconstitutional" and "not based on law."
"Telegram's position remains the same -- the FSB's request is...impossible to carry out, both in technical and legal terms, and therefore the request to block [Telegram] is groundless as well," Akhmetgaliyev said.
Akhmetgaliyev added that he had not yet seen Roskomnadzor's lawsuit and could not comment on it specifically.
Putin's spokesman, Dmitry Peskov, told reporters that the Kremlin considered Telegram "very convenient to use, including for communication with journalists," and that "it will be a pity if a consensus is not reached."
"The law is the law, and if it is not followed and corresponding measures are taken, we will look for an alternative [to Telegram] that best suits our needs," said Peskov, who told RFE/RL in March that he uses Telegram for some communications with journalists.
On March 20, Roskomnadzor ordered Telegram to provide the FSB with encryption keys needed to read users' messaging data within 15 days, after the Supreme Court rejected Telegram's challenge to the demand.
Telegram has been defiant throughout the showdown. Co-founder Pavel Durov, who lives in self-imposed exile abroad, said after the Supreme Court ruling that his company would not provide the FSB with encryption keys.
"Threats to block Telegram unless it gives up private data of its users won't bear fruit. Telegram will stand for freedom and privacy," Durov wrote on Twitter at the time.
Kremlin critics have used social media to spread the word about antigovernment demonstrations and to publicize corruption allegations against Putin, a former FSB chief and Soviet KGB officer, and his allies.
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 Russian Internet entrepreneur Durov and his brother in 2013.
It has become an influential forum for news and debate, featuring popular channels run by news sites, journalists, and political analysts.
Roskomnadzor's March 20 request came shortly after the Supreme Court rejected Telegram's complaint against the FSB's 2016 order obliging it to provide encryption keys.
Telegram's lawyers said at the hearing that the FSB order violated the privacy of correspondence. FSB representatives said the agency did not consider information exchanged via messenger apps to be protected by privacy legislation.
A Moscow court in October imposed an 800,000-ruble ($13,800) fine on Telegram for its refusal to provide the FSB with encryption keys.
In 2014, Durov announced that he had left Russia after he was forced to sell his stake in the social network VKontakte under pressure from the authorities.
Durov said in September 2017 that the FSB had notified him that his firm was in violation of counterterrorism laws requiring companies to provide access to encrypted communications they facilitate.
He said at the time that Russian authorities were pressuring Telegram to comply with controversial legislation known as the Yarovaya laws.
Rights groups call the laws a draconian infringement on privacy that can be used to stifle dissent, and Durov called them unconstitutional.