Russian PM, Vladimir Putin
Dozens of Russian opposition activists, including writer Eduard Limonov, were on Saturday arrested during unauthorised gatherings in Moscow and St Petersburg.
In Moscow, around 300 people, some shouting "Russia without Putin" gathered in Triumfalnaya Square.
Police called on the activists to disperse, pushing them towards adjacent streets, and arrested around 20 people, an AFP photographer witnessed.
A police officer suffered burns to the face as a result of a smoke bomb allegedly thrown by a demonstrator, police said.
The rally was part of the opposition's long-running campaign to uphold Article 31 of the Constitution which guarantees freedom of assembly.
Limonov, leader of a nationalist left-wing opposition group, was also arrested and taken to a police vehicle, Interfax said.
In Saint Petersburg, about 60 people tried to stage a demonstration but were dispersed by police who detained 15 people, according to police.
Earlier in Moscow's Pushkin Square around 100 people gathered for a "meeting" organised by far-left activist Sergei Udaltsov of the Left Front movement.
But when two activists tried to unfurl a banner, they were arrested, the Ria Novosti agency said. Another was detained after allegedly attacking pro-Kremlin activists who had come to recite Russian poetry.
The Interfax agency said activists hostile to the opposition supporters had assembled to "pray" near the gathering.
Vladimir Putin, having just served as prime minister, was elected for a third presidential term in a March 4 election with over 63 percent of votes despite months of protests against his regime.