By Alissa de Carbonnel
MOSCOW (Reuters) - Russia's top social networking site on Thursday defiantly rejected a request by the Federal Security Service to block opposition groups from using it to organize street protests accusing the authorities of rigging this week's election.
Over 45,000 people in Moscow alone have pledged on Facebook and the Russian site, VKontakte, to join fresh protests on Saturday against the 12-year rule of Vladimir Putin and the victory of his United Russia party in Sunday's parliament vote.
The move by the Federal Security Service (FSB), successor to the Soviet KGB, was reminiscent of attempts by some Arab governments to sever online communication between protesters.
"We received a request from the FSB asking us to close activities by groups calling to make noise on the street, to organize a revolution," VKontakte spokesman Vladislav Tsyplukhin said in e-mailed comments.
Defying the request, Tsyplukhin said: "We can't block groups simply because some individual users call for violence."
He added that VKontakte, which has 100 million registered users, was not pressured or threatened by the FSB in any way.
The FSB declined to comment when contacted by Reuters.
In a country dominated by state-run media, amateur smartphone videos and online testimonies of ballot stuffing and multiple voting in Sunday's election have been instrumental in galvanizing protesters.
Prime Minister Putin accused the United States earlier on Thursday of stirring up the protests, which threaten to sully his image three months before a presidential election in which expected to return to the post he held from 2000 to 2008.
Choreographed political events broadcast on state television, as when Putin said in September he would swap jobs with President Dmitry Medvedev, have fuelled disenchantment and drawn comparisons to Soviet-era Communist party meetings.
On the Internet in Russia, where London market research firm ComScore says people spend more hours on social networking sites than anywhere else in the world, a starkly different picture is emerging.
Many bloggers now fear the authorities will crack down. In recent days, mass cyber attacks crippled the country's top blogging platform LiveJournal and the sites of liberal media outfits which reported on campaign violations.
"Now the connection between hackers and state government activity seems to be more clear," said Andrei Soldatov, a Russian intelligence expert from Agentura.ru, which tracks Russia's special services.
"Clearly we now see panic. They have no strategy for how to deal with Facebook," he said. "They have focused for many, many years on methods and tactics to prevent any kind of demonstrations and street riots."
The United States said in its 2010 human rights report that Internet systems route Russian web traffic to the FSB.
Soldatov said many senior Russian agents in the security services see social media sites as a tool of the West created to "change political regimes."
Earlier this year a senior FSB official called Gmail, Hotmail and Skype "a major threat to national security," but Putin dismissed the comment, saying he had no plans to crack down on the Internet before 2012 elections.
The head of Russia's cyber crimes unit warned that people did not realize how dangerous social media sites were in creating disorder, citing as an example ethnic riots near Red Square nearly a year ago.
"We underestimate the danger," Major General Alexei Moshkov told the state Rossiiskaya Gazeta daily in an interview published on Thursday.
"We all remember what happened at the end of last year (and) it is social media sites, where extremist slogans and calls for action were voiced, which led to the riots."
(Editing by Amie Ferris-Rotman and Mark Trevelyan)