Russia’s opposition is holding rallies to protest against what it says were rigged elections on 4 December.
In the first of the day’s rallies in the far eastern city of Vladivostok, regional MP Artyom Samsonov said the election results should be cancelled.
In the capital, Moscow, organisers expect some 50,000 people to gather on Sakharov Avenue in the city centre.
President Dmitry Medvedev announced political reforms this week, but many demonstrators say it is not enough.
They are demanding a re-run of the poll, which was won by the party of Prime Minister Vladimir Putin – but with a much smaller share of the overall vote.
In Vladivostok, demonstrators carried posters calling for Mr Putin to be put on trial.
