Russian internet monitoring services reported a mass outage on the availability of video hosting site YouTube on Thursday as Russian authorities step up criticism of the platform.

Russian internet monitoring service Sboi.rf said there had been thousands of glitches reported about YouTube in Russia. Users said they could only access YouTube via virtual private networks (VPNs).

"YouTube is not working," one anonymous user said in comments on the site.

Reuters reporters in Russia were unable to access YouTube. The website remained available via some mobile devices.

Google did not immediately respond to a request for comment on Thursday. Russia’s state communications watchdog Roskomnadzor also did not immediately reply to a request for comment.

YouTube is one of the last major bastions of free expression on the Russian internet, where the site continues to host materials by Kremlin opponents that have been largely removed from other social media sites popular in Russia.

The site's download speeds have notably slowed in recent weeks, for which Russian lawmakers have blamed YouTube owner Alphabet's Google, something the company disputes.

Alexander Khinshtein, head of a parliamentary committee on information policy, warned last month that YouTube speeds would drop by as much as 70%.

He said the degradation was "a necessary step, directed not against Russian users, but against the administration of a foreign resource that still believes it can violate and ignore our legislation without punishment."

Khinshtein later explicitly blamed the slowdown on Google's failure to invest in Russian infrastructure, such as its local cache servers, something YouTube rejected.

A YouTube spokesperson said last week it was aware of reports that some people were unable to access YouTube in Russia. This was not because of any actions on technical issues on its part, it said.