Whistle-blower Alexei Navalny, leftist leader Sergei Udaltsov, liberal politician Ilya Yashin and political activist Ksenia Sobchak were arrested at an event in Lubyanka Square recognizing victims of political persecution in the Soviet Union, RIA Novosti reported.
Several sanctioned rallies were held at other cities across Russia, but the rally in Moscow was not approved by City Hall, which gave police the power to detain people at the square, officials said.
RIA Novosti said Udaltsov was detained during a speech he was giving; Yashin and Sobchak were stopped as they approached the rally, and Navalny was arrested after he gave a speech.
Police estimated about 500 people attended the rally, but several media outlets were reporting participants numbered in the thousands.
Beyonce flaunts bikini body, Blue Ivy in vacation pics
Benedict Cumberbatch's dramatic reading of R. Kelly lyrics is just what you need