Originally posted by the Voice of America. Voice of America content is produced by the Voice of America, a United States federal government-sponsored entity, and is in the public domain. May 06, 2012 Russian Police, Protesters Clash at Anti-Putin Rally VOA News Participants sit down on the street during the "march of the million" opposition protest in central Moscow, May 6, 2012. Photo: Reuters Participants sit down on the street during the "march of the million" opposition protest in central Moscow, May 6, 2012. Russian riot police clashed with demonstrators Sunday as an estimated 20,000 people protested on the eve of Vladimir Putin's inauguration for a third presidential term. Helmeted officers beat protesters with batons and hauled away dozens after skirmishes broke out between the two sides near a bridge leading across the Moscow river to the Kremlin. Those detained include three key leaders in the protest movement against Putin - Alexei Navalny, Boris Nemtsov and Sergei Udaltsov. Officials say at least four officers were injured. Putin has been Russia's prime minister since relinquishing the presidency in 2008. He won the country's March 4 presidential election by a landslide, but the opposition disputes the victory, calling it a stolen election. World leaders acknowledged Putin's victory with reservations, and international observers say the election was clearly skewed in the former president's favor. Some information for this report was provided by AP, AFP and Reuters. .