Twitter is being restricted for some users in Russia, the social media company said in a tweet on Saturday.
On Friday, one day after Russia invaded Ukraine, Moscow said it was partially limiting access to Meta Platforms Inc's Facebook, accusing it of "censoring" Russian media.
Twitter said it was working to keep its service safe and accessible. It did not immediately respond to a question on whether Russia had communicated with the company about any actions.
Internet blockage observatory NetBlocks reported that Twitter had been restricted on leading networks. A Reuters reporter in Moscow on Saturday said the site was slow and had difficulties sending tweets.
Russia has been trying to exert tighter control over the internet and big tech companies for years, in efforts that critics say threaten individual and corporate freedom, and are part of a wider crackdown against outspoken opponents of the Kremlin.
Last year, Moscow slowed down the speed of Twitter in a punitive move because it said the site was not removing illegal content.