Russia's media watchdog, Roskomnadzor, has imposed restrictions on Twitter by slowing down, or throttling, its speed across the country for its "failure" to remove banned content.
Roskomnadzor said in a statement placed on its website on March 10 that the measure is meant "to protect Russian citizens from the influence of illegal content." It threatened to fully block the U.S. social network if it did not act.
The action comes amid efforts to tighten control of social media and a clampdown on platforms that have been used to organize protests in support of jailed Russian opposition leader Aleksei Navalny.
According to Roskomnadzor, as of March 10 Twitter had 3,168 posts with banned content on its site, including more than 2,500 posts encouraging suicide among minors. The Roskomnadzor statement also referred to content on illegal drugs and pornography.
"One hundred percent of mobile gadgets and 50 percent of non-mobile devices will be affected by the measure to slow the service down. If Twitter continues to ignore the requirements of the law, enforcement measures will be continued in line with the response regulations [up to fully blocking the site]," Roskomnadzor's statement added.
Roskomnadzor deputy chief Vadim Subbotin confirmed to the Interfax news agency on March 10 that the watchdog had the "technical capacity" to slow Twitter inside Russia and that it had already started to do so.
Kremlin spokesman Dmitry Peskov said the government had "no desire to block anything," but added that it was "quite reasonable" for the authorities to enforce compliance with the law.
Twitter said it was "deeply concerned by increased attempts to block and throttle online public conversation" and said it did not support unlawful behavior.
"We have a zero-tolerance policy regarding child sexual exploitation," Twitter said in a statement, adding that it is against Twitter's rules to "promote, glorify or encourage suicide and self harm."
While Twitter users may have found slower service, a number of government websites -- including the Kremlin's -- were unavailable altogether for some Russian Internet users, though officials quickly noted they were not caused by new restrictions imposed on the social network.
Netblocks, a web-outage monitor, confirmed the slowdown on Twitter.
"Real-time network data show elevated latency to Twitter servers from #Russia with high impact to mobile internet providers and some fixed-line networks, consistent with targeted traffic shaping or throttling; incident ongoing," Netblocks said on Twitter.
Roskomnadzor's Subbotin warned that "it is possible" similar measures could be imposed against other social networks such as Facebook in the future if they did not follow Russian regulations,
Moscow has been trying to curb social media in recent years amid increasing protests among Russias, especially younger ones, and social media's role in amplifying dissent.
Officials in January accused foreign Internet companies of interfering in Russia's domestic affairs over their failure to take down calls to participate in rallies in support of Navalny.
The government has previously moved to tighten control of social media by requiring online services to store the personal data of Russian users on servers in Russia. Facebook and Twitter have been fined for failing to comply with the law.
Russian Foreign Ministry spokeswoman Maria Zakharova late last year accused Facebook and Twitter of "open censorship" after they blocked Russian accounts and content and after Twitter labeled government and state-affiliated media accounts.
Late last month Roskomnadzor demanded Twitter explain why it removed 100 accounts linked to Russia.
Twitter said in response that the accounts "amplified narratives that were aligned with the Russian government, focused on undermining faith in the NATO alliance and its stability," and targeted the United States and the European Union.
On February 1, a Russian law came into force that states social networks must themselves find and delete content banned by Russian law.
If a social network is unable to determine if content contains banned materials, it must send the content to Roskomnadzor for an evaluation.