* Alisher Usmanov's Mail.Ru buys 12 pct stake in VKontakte
* Becomes controlling shareholder with 52 percent stake
MOSCOW, March 18 (Reuters) - Billionaire Alisher Usmanov cemented his control over social media in Russia on Tuesday, increasing his ownership of the country's biggest networking site VKontakte in a deal that helps the Kremlin tighten its grip on the media.
Usmanov, a Kremlin ally, is one of two men who have come to dominate media ownership in Russia, and increasingly the social media, since President Vladimir Putin rose to power in 2000.
His Internet holding group Mail.Ru said it had increased its stake in VKontakte, Russia's answer to Facebook , to around 52 percent by buying 12 percent of VKontakte (VK) shares from Megafon Chief Executive Officer Ivan Tavrin.
Mail.Ru already owns Russia's No. 2 and 3 social networking sites - Odnoklassniki (OK) and Moi Mir (My World) - and the deal for a further stake in VK gives it effective control over the top three social media in Russia.
Usmanov, worth $18.6 billion according to U.S. magazine Forbes, also owns Russian business daily Kommersant among other investments in telecoms and an iron ore and steel producer.
Mail.Ru said in a statement that no changes to the operational control over VK were intended and that it did not plan to fully consolidate VK in its financial statements.
Russia, with the largest Internet audience in Europe, has tightened monitoring of user-generated content since activists used social networks to organise protests over the December 2011 parliamentary election, which handed victory to Putin's ruling United Russia party.
The measures included launching a black list of sites distributing content such as child pornography, but which critics have said could boost censorship.