Russia's Vladimir Putin takes office Monday for a historic third presidential term.

Police have tightened security in the capital, Moscow, ahead of the inauguration.

Mr. 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. The opposition disputes the victory, calling it a stolen election.

World leaders acknowledged Mr. Putin's victory with reservations, and international observers say the election was skewed in the former president's favor.

Russian riot police clashed with demonstrators Sunday as an estimated 20,000 people protested against Mr. Putin.

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.

Three key leaders in the protest movement against Mr. Putin – Alexei Navalny, Boris Nemtsov and Sergei Udaltsov -were among the detained. Officials say at least four officers were injured.

###