“Access to the messaging app Signal was blocked in connection with a violation of the requirements of Russian legislation, which must be observed to prevent the use of messaging apps for terrorist and extremist purposes,” Interfax quoted the agency as saying.

Before Roskomnadzor announced measures, hundreds of Signal users had reported disruptions to the messaging app, a secure communications tool used by up to a million Russians to encrypt messages and conversations.

Internet service monitoring sites have recorded more than 1,500 complaints about Signal, most of them from users in Moscow and St. Petersburg. However, users reported that Signal worked normally when accessed through a VPN or used in the built-in censorship bypass mode.

“This indicates precisely a blocking of the messenger in Russia and not a technical problem on the Signal side,” Mikhail Klimarev, author of the Telegram channel “For Telecom,” told Reuters.

Signal did not respond to a request for comment.

It was also not possible to register a new account with Signal without a VPN, three people from Moscow and the Krasnodar region told Reuters. When entering a mobile phone number, the service displayed the message “Server error”.

Klimarev said it was the first attempt to block Signal in Russia.

Russian authorities began blocking access to Telegram, a widely used messaging app, in 2018. This measure disrupted many third-party services but had little impact on Telegram’s availability in Russia.