The development came as Roskomnadzor told Navalny -- along with YouTube and Instagram -- that they must delete or block access to a video and photos in an online report about an alleged meeting between billionaire Oleg Deripaska and Deputy Prime Minister Sergei Prikhodko, a longtime former senior adviser to President Vladimir Putin.
Navalny defied the order, which followed a court ruling that publication of the video and photos violated the privacy rights of Derispaska, who filed a lawsuit over the matter after Navalny posted the report on his website on February 8.
Navalny's report, which he says is part of a growing body of evidence of corruption in circles close to Putin, draws on photos and videos published earlier on the social-media account of a Belarusian woman who goes by the name Nastya Rybka and says she had an affair with Deripaska.
A February 14 deadline that Navalny said was set by Roskomnadzor passed without incident, but reports that navalny.com was inaccessible for many in Russia began flowing in on February 15.
"The first reports that navalny.com does not open have come in," Navalny tweeted, and other Internet users said on Twitter that they were unable to open the site through major Russian Internet providers.
"Roskomnadzor has begun blocking navalny.com at the behest of Deripaska. The site still opens through some providers, but that is temporary," Navalny, who has accused Roskomnadzor of "censorship," said in a subsequent tweet.
Later on February 15, however, senior Navalny associate Leonid Volkov tweetedthat the site was widely accessible, calling Roskomnadzor "cretins" and saying that "the 'blocking' mechanism can be broken with little effort."
Meanwhile, the Interfax news agency reported that Roskomnadzor was pressing its demand that U.S. Internet giant Google delete or block access to the videos and photos on YouTube.
"Roskomnadzor expects a decision from...Google on the deletion from YouTube of the materials [referred to] in the court decision. Roskomnadzor hopes that Google's decision will be positive," Interfax quoted the regulator's press service as saying. It said that the material "has been deleted" from Instagram.
There was no immediate comment from Google.