MOSCOW - Russia on Friday charged protest leader Sergei Udaltsov with plotting mass riots in a controversial probe that has seen the detention of another activist who claims to have been tortured into confessing. Udaltsov was charged after being summoned by the Investigative Committee for questioning over an alleged plot to hold mass riots with international funding to topple President Vladimir Putin. Two men have already been charged in the probe, including Leonid Razvozzhayev, an aide to an opposition parliamentary lawmaker, who has retracted a confession that he said he made under pressure after being kidnapped by Russian security agents in Ukraine.