Russia’s communications watchdog said Monday it has begun enforcing a nationwide ban for the popular messaging app Telegram.

Telecommunications providers have been instructed to block Telegram in Russia after a court last week sided with authorities who demanded that the app be kept of the country until it hands over the keys to its data encryption.

Russian authorities alleged that Telegram, which was developed by Russian entrepreneur Pavel Durov, has been used by violent extremists. The company argues that Russia’s FSB intelligence service is violating consumer rights.

Telegram was briefly unavailable to users early Monday afternoon, but was back online later in the day. Durov said last week the latest version would have “built-in” features that would be able to circumvent the ban.

“We consider the decision to block the app to be unconstitutional and we will continue,” he said in a statement posted on social media Monday.

Privacy features have made Telegram the messaging app of choice for many Russian officials. The Kremlin has used it for arranging conference calls with reporters.

The Russian president’s press office said Monday it would now be using a different app.

(AP)