Russia's media watchdog has said it is slowing down the speed of Twitter, accusing the US social media company of failing to remove 3,000 posts relating to suicide, drugs and pornography.
The move was intended to protect Russian citizens, Roskomnadzor said.
Twitter is widely used by the Kremlin's opponents and Russian users said they were having difficulty accessing photos and videos on the site.
The company said it was "deeply concerned" by the watchdog's decision.
Media watchdog officials said the disruption, which affected a number of Russian websites including the Kremlin, was unrelated to the action against Twitter and involved technical issues at Russian state internet provider Rostelecom, which was also affected.
The watchdog said it was reducing the speed of Twitter on all mobile phones in Russia and on half of desktop devices. It cited Twitter's failure to remove banned content which, it said, incited the suicide of minors and contained indecent images of children, as well as information on drug use.
There were reports that internet connection speeds in general had slowed down.
Twitter is the sixth biggest social media site in Russia and widely used by opposition figures including Alexei Navalny, who was jailed in January on his return to Russia after treatment for a poisoning attack in Siberia.
