A leading Russian human rights activist has complained about the arrest of more than 120 people at opposition rallies in Moscow and St Petersburg.
Lyudmila Alexeyeva said there was no point obtaining permission to protest if people were detained regardless.
Opposition leader Boris Nemtsov was among those detained during the rallies on New Year's Eve.
The authorities said those arrested in Moscow were going to another, unauthorised demonstration.
Police in Moscow detained 68 people, while more than 50 were arrested at the St Petersburg demonstration, which did not have a permit.
The rallies take place regularly on the 31st day of the month to highlight Article 31 of the Russian constitution, which protects the right to freedom of assembly.
Mr Nemtsov, once first deputy prime minister, described Mr Putin as a threat to Russia. He was arrested when he attempted to break through police lines, police said.
Protesters at the Moscow rally also demanded that Prime Minister Vladimir Putin stand down and called for the release of former tycoon Mikhail Khodorkovsky, an outspoken critic of the Kremlin.
Many of the protesters were dressed as Father Frost or the Snow Maiden, traditional Russian characters. Among them was Ms Alexeyeva, at 83 one of Russia's most respected human rights activists.
Ms Alexeyeva, head of the Moscow Helsinki Group, called on the fractured opposition to unite against the government.
Russia has rejected foreign criticism of Khodorkovsky's imprisonment, which was extended for another five and a half years after his second trial concluded on Thursday.