On the eve of Vladimir Putin's return to Russia's highest office --- at least 20,000 people gathered in Moscow in protest.

Yelling "we are not leaving," protesters attempted to march toward the Kremlin but were met by lines of riot police.

Officers used batons to try and beat back advancing demonstrators and detained dozens.

The violence came at the end of a day of protests in several cities. Putin will be sworn in for a third term as president on Monday.

Deborah Gembara, Reuters.