In a sign of new limits on Facebook’s ability to serve as a platform for political opposition movements, Russian users appear to have been blocked from accessing a page calling for a protest in support of a prominent dissident.

In 2011, Facebook was hailed by opposition movements during the Arab Spring and in Russia as a powerful new tool to spread information beyond the control of repressive governments. That may no longer be the case, at least not in Russia. Russian Internet regulators said Saturday that they had sent Facebook a “demand” that it block access to a page calling for a demonstration in support of Alexei Navalny, the most prominent critic of Russian President Vladimir Putin….

“At the moment, the demand” to block the page “is being fulfilled” by Facebook, Vadim Ampelonsky, a spokesman for the Russian Internet regulator, told the Interfax news service.