Facebook has been accused of succumbing to pressure from the Kremlin to censor a page set up in support of an opposition figure in Russia.
A page rallying support for Alexei Navalny, arguably Vladimir Putin's most prominent opponent, appears to have been blocked to users in Russia.
Former US ambassador to Russia Michael McFaul said the move was a "horrible precedent".
Facebook has repeatedly declined to rule out that it was responsible for disabling the page in Russia - a spokeswoman instead pointed out that users in the country could still access similar content about Navalny, who is facing jail.
Under the circumstances you’d expect the leaders of Facebook to at least explain what’s happened.
- Tanya Lokshina, Russia programme director at Human Rights Watch
New laws being drawn up in Moscow now could see all foreign-hosted social networks banned next year.
Facebook is not the most popular social network in Russia - that accolade going to predominantly Russian-language VK.
More: [Facebook considering developing tech to stop you drunk posting]1
More: [Activist jailed for three years for asking judge if he used Facebook]2
More: [What you missed at Vladimir Putin's quite crazy press conference]3