Russia has blocked the popular Tor network that allows users to remain anonymous online.
The country's state communications watchdog, Roskomnadzor, confirmed on Wednesday it has blocked access to the Tor service.
The authority said the move followed the "dissemination of information on the site ensuring the operation of services that provide access to illegal content".
It is the latest development in a series of moves as Moscow aims to tighten its grip on the Russian internet.
The Kremlin says their efforts are to combat online extremism and terrorism, but critics say that Russia is stifling free speech and attempting to control political debate.
The Tor network -- developed in the United States -- uses encryption to evade surveillance by masking a users' internet provider (IP) from the authorities.
According to the Tor Project, Russian users are the service's second-largest audience, with over 300,000 users per day or 15% of all users of the service.
Tor also allows users to access the so-called "dark web" without the need to use a virtual private network (VPN).
In September, Roskomnadzor had already blocked six VPNs that allowed Russian users to access a growing number of banned websites.
The authorities have also increased pressure on big tech giants -- such as Twitter, Apple, and Google -- ordering them to remove "illegal" content.
In July, Russian President Vladimir Putin also enacted a law that forces foreign technology giants to open representative offices in the country if they do not want to suffer sanctions or blockades.