Recasts with comments from head of FSB security service

MOSCOW, Feb 19 (Reuters) - The head of Russia's FSB security service accused Telegram founder Pavel Durov on Thursday of condoning criminal activity on the app, in an escalation of Moscow's rhetoric as it moves to throttle the messaging platform.

Russia's state communications regulator has introduced restrictions on Telegram, which is hugely popular in Russia for both public and private communications, over what it says is a failure by the company to delete extremist content.

Telegram has responded, accusing Russian authorities of using false pretexts in an attempt to cripple its operations in order to promote a new state-owned messenger called MAX.

In comments to a Russian journalist, FSB chief Alexander Bortnikov was quoted on Thursday as saying that Durov, Telegram's Russian-born founder, "is pursuing his own mercenary interests, which are ultimately realised through a large number of legal violations."

Bortnikov said crimes committed through Telegram included juvenile delinquency, terrorist attacks, and sabotage, and that Durov's approach amounted to "condoning what is happening".

He said previous attempts to talk with Durov had been fruitless.

Telegram did not immediately respond to a request for comment on Bortnikov's comments.

TELEGRAM DENIES MINISTER'S ENCRYPTION BREACH ALLEGATION

The communications regulator moved this month to slow down Telegram and impair its functionality, saying it had failed to respond to previous warnings.

And on Wednesday, a government minister raised another purported reason not to trust Telegram, alleging that foreign intelligence services could read messages sent by Russian soldiers over the app.

The company strongly denied that in a statement to Reuters, saying "no breaches of Telegram's encryption have ever been found."

Russian soldiers, war correspondents and politicians have said Telegram is widely used by troops fighting in Ukraine - not only to communicate with their families back home, but also sometimes for operational purposes.

"The Russian government's allegation that our encryption has been compromised is a deliberate fabrication intended to justify outlawing Telegram and forcing citizens onto a state-controlled messaging platform engineered for mass surveillance and censorship," the company said.

Russian authorities have also blocked or restricted other foreign messaging platforms, including Meta's META.O WhatsApp and Apple's AAPL.O FaceTime.

They have urged Russians to switch to MAX, the new app, and have rejected allegations that it is designed as a surveillance tool.

Despite the campaign against Telegram, Russian authorities including the Kremlin and defence ministry continue to publish information on the app.

Ordinary people, meanwhile, can circumvent the restrictions on it by using a virtual private network.

(Reporting by Gleb Stolyarov; Writing by Mark Trevelyan; Editing by Joe Bavier)

((moscow.newsroom@thomsonreuters.com;))