Meta platforms including Facebook and Instagram have been blocked by Russia, the country's communications regulator has confirmed.
The regulator, Roskomnadzor, claimed the decision was in response to restrictions of access to Russian media on the platform.
It said there had been 26 cases of discrimination against Russian media by Facebook since October 2020, including restrictions in recent days on state-backed channels like RT and the RIA news agency.
The move is a major escalation in an ongoing confrontation between big tech companies and Russia, which has in recent years issued a slew of fines and hobbled services through slowdowns.
The tensions have ramped up amid Russia's invasion of Ukraine, which Moscow calls a "special operation."
Meta's head of global affairs Nick Clegg said the company would continue to do everything it could to restore its services.
"Soon millions of ordinary Russian will find themselves cut off from reliable information, deprived of their everyday ways of connecting with family and friends and silenced from speaking out," he said, in a statement posted on Twitter.
Last week, Moscow said it was partially limiting access to Facebook, a move the company said came after it refused a government request to stop the independent fact-checking of several Russian state media outlets.
Twitter also said its service was being restricted for some Russian users but it is understood there is currently nothing to suggest the platform has been blocked in the country.
Major tech companies have faced pressure to respond to the February 24 invasion, which has led to economic sanctions against Moscow by governments around the world. Russian state-run media has emerged as a key flashpoint between Moscow and social media platforms during the conflict.
Meta this week said it had restricted access to RT and Sputnik across the European Union and was globally demoting content from Russian state-controlled outlets' Facebook pages and Instagram accounts, as well as posts containing links to those outlets on Facebook.
Tech companies such as Alphabet Inc's Google have also paused advertising in Russia.
Russia has made several moves to crack down on foreign news media in recent days. It cut access to several news organisations' websites, including the BBC, Voice of America and Radio Free Europe/Radio Liberty for spreading what it says is false information about its actions in Ukraine.
Ukraine's government had called on Meta and other platforms during the conflict to withdraw their services from Russia.
Online speech experts and rights advocates have raised concerns about the impact of blocking online services for Russian citizens trying to organise or get information.
Meta had about 7.5 million users on Facebook in Russia as of last year and 122.2 million users across its other services, including Instagram, WhatsApp and Messenger, according to estimates from Insider Intelligence.
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