MOSCOW, June 26 (Reuters) .

Russia's FSB security service said on Monday that terrorists had used the telegram messaging app to carry out a deadly suicide bombing on Russian soil, increasing pressure on the app days after the authorities accused it of breaking data laws.

Russia's communications regulator Roskomnadzor said on Friday it would block telegram soon unless it handed over information needed to put the app on an official government list of information distributors.

telegram has so far refused to comply because it fears complying would undermine the privacy of its more than 6 million Russian users.

Once on the list, it would have to store information about its users on Russian servers and hand over user information to the authorities on request.

The FSB, the successor agency to the Soviet-era KGB, weighed into the standoff on Monday, releasing a statement which said telegram provided "terrorists with the opportunity to create secret chat rooms with a high degree of encryption."

It said a suicide bomber who blew himself up on the St Petersburg metro on April 3, killing 15 people, had used telegram to plan the attack with his accomplices, and that telegram had become the most widely used app of its kind by terrorists operating inside Russia.

The intervention suggests the authorities are serious about blocking telegram on national security grounds unless its meets their demands.
Pavel Durov, telegram's founder, said the app had blocked thousands of terrorism-related channels and that if Russia banned it, terrorists would just switch to a competing service.

"The appearance of information saying that telegram was allegedly used to prepare an act of terrorism three months ago raises questions," Durov wrote on social media on Monday.

"It's sad if Russia's intelligence services are exploiting such a tragedy as a pretext to strengthen their influence and control over the population."
Alexander Zharov, head of the communications regulator, told state-backed NTV on Sunday that telegram had just days to comply and accused Durov of being an anarchist with no interest in respecting the law.

"As far as I know, Mr Durov's unwillingness to hand over the keys to the information to the world's intelligence services allows terrorists to kill people with impunity using this channel of communications," said Zharov.

'ANTI-CONSTITUTIONAL?'

Durov, 32, has clashed with the authorities before, refusing to comply with various data requests related to the VKontakte social media site which he set up after leaving university. That row ended with him selling up and leaving the country.

The Kremlin said the latest dispute was purely a matter for the communications regulator. If telegram was banned, Dmitry Peskov, President Vladimir Putin's spokesman and an avid telegram user, said he and other officials would switch to another service.

Durov said the communications regulator's demands violated Russians' constitutional right to keep their correspondence secret and were also technically impossible to comply with.

He said telegram was doing its best to help fight terrorism and that blocking it would not help because other encrypted services were available.
"If you want to defeat terrorism by blocking stuff, you'll have to block the Internet," wrote Durov.