Russia has exerted increasing pressure on foreign tech companies this year over content shared on their platforms and has also targeted virtual private networks (VPN) and other online tools in a campaign critics say stifles internet freedom.

The regulator, Roskomnadzor, said the website www.torproject.org had been prohibited on the basis of a court decision.

“The grounds for this were the placement of information on this website that enable the operation of tools that provide access to unlawful content,” Roskomnadzor said in a statement.

“Today, access to the resource has been restricted.”

Tor, which was founded by U.S. computer scientists, said that without access to its service hundreds of thousands of people would no longer have a safe way to communicate both within Russia and globally.

The Tor anonymity network is used to hide computer IP addresses to conceal the identity of an internet user. Tor, which says its mission is to advance human rights and freedoms, says it has more than 300,000 users in Russia, or 14% of all daily users, second only to the United States.

Reuters verified that the Tor website was inaccessible. There was limited access to the Tor browser and other elements of the Tor infrastructure.

GlobalCheck, a group that monitors websites’ accessibility in Russia, confirmed that blocking had begun.

In a blog post published on Tuesday, Tor said some internet providers had started blocking access since Dec. 1 and urged its users to circumvent the block by visiting its mirror site, which was still working.

“Blocking Tor would be practically impossible. It is a large community which will find the means to finance the organisation of getting around blocking in Russia,” said Mikhail Klimarev, head of the Internet Defence Society, a non-profit group seeking to fight online censorship in Russia.

Anton Gorelkin, a member of Russia’s State Duma committee on information and communications, this week described Tor as a cover for illegal activity and an “absolute evil”.

Tor responded: “By making a comment that dismisses the need for such technology, or by trying to portray it in this way, governments obscure the reality: Tor and technology like it are lifelines.” (Reporting by Alexander Marrow, Gleb Stolyarov and Anton Zverev; Editing by Elaine Hardcastle, David Evans and John Stonestreet)