The Other Russia -- ranging from pro-Western liberals to radical leftists -- dubbed its protest Saturday the "March of Dissent." Another, similar march is planned in the northern city of Saint Petersburg on Sunday.
"We are pushing for change through elections. But we want real, free elections, not imitations, in our country," Kasyanov told supporters.
The demonstration comes after one of Putin's most outspoken critics, multi-millionaire Boris Berezovsky, said he was planning a "revolution" from his exile in London.
MORE: H.E Mart Helme points out in The Brussels Journal that there's more going on in Russia than just upcoming elections.
MORE: The debate over dictatorship and economy.