Russia has limited Twitter in parts of Russia, Twitter has confirmed.
In a statement, the company said "We're aware that Twitter is being restricted for some people in Russia and are working to keep our services safe and accessible".
On Friday Russia restricted Facebook after a clash over "censorship".
Russia's communications regulator Roskomnadzor accused Facebook of violating "the rights and freedoms of Russian citizens".
Facebook said it had refused to stop fact-checking and labelling content from state-owned news organisations.
Internet connectivity watchers at NetBlocks say there is a total or near-total restriction on Twitter in Russia.
NetBlocks said Facebook and Instagram weren't "observably restricted per our metrics, certainly not to the extent Twitter is at present".
The actions follow Russia's attack on Ukraine with many videos and images of the invasion going viral on social media.
The BBC's Moscow correspondent, Steve Rosenberg, said he'd had difficulty tweeting.
Circumvention for those in Russia is currently possible using VPN services, which can work around government-imposed restrictions.
NetBlocks Director Alp Toker told the BBC: "Russia's restriction of Twitter will significantly limit the free flow of information at a time of crisis when the public most need to stay informed."
Roskomnadzor has not announced actions against Twitter.