Telegram's Russian founder has vowed to reject any attempt by the security's services to gain backdoor access to the app

Russia's telecoms watchdog on Friday asked a Moscow court to block the popular messaging app Telegram after the expiry of a deadline for it to give the state security services access to private conversations.

The lawsuit is the latest move in an ongoing battle between authorities and Telegram, which has a reputation for secure communications, as Moscow pushes to increase surveillance of internet activities.

Roskomnadzor said in a statement it had filed a suit "demanding the limiting of access on Russian territory" to the service.

But a lawyer representing Telegram said any ban would be unconstitutional and in any case impossible to enforce.

"The position of Telegram remains the same—the demands of the FSB (security service) to provide access to private conversations of users are unconstitutional, not based on the law, and cannot be fulfilled technically and legally," said Pavel Chikov, who leads a human rights group representing the app.

Telegram's self-exiled Russian founder Pavel Durov has long said he would reject any attempt by the country's security services to gain backdoor access.

The free application, which lets people exchange messages, photos and videos in groups of up to 5,000 people, has attracted some 200 million users since its launch in 2013.

President Vladimir Putin's spokesman Dmitry Peskov on Friday said the service was a convenient tool to communicate with journalists and it would be a "shame" if an agreement between the app and authorities could not be reached.

"But the law is the law," he added during a regular briefing, quoted by Interfax news agency.

Telegram is popular among political activists of all stripes, but has also been used by jihadists.

"In Russia we have many problems—from poverty to awful state of the roads, from crime to poor medical care," opposition leader Alexei Navalny said via Twitter.

"But the state is engaged in blocking Telegram in our name ...in what way is Telegram making life in Russia any worse? Whom is it bothering?" he said.

In September 2017 the FSB demanded the encryption keys, Durov said, prompting a formal complaint when the request was rejected.

The Roskomnadzor had threatened to ban the app in June last year for failing to provide its registration documents. Although Telegram later registered, it stopped short of agreeing to the regulator's data storage demands.

Companies on the register must provide the FSB with information on user interactions.

From this year they must also store all the data of Russian users inside the country, according to controversial anti-terror legislation passed in 2016 which was decried by internet companies and the opposition.

Explore further Telegram must give FSB encryption keys: Russian court

© 2018 AFP