Police arrested anti-Kremlin opposition leader Boris Nemtsov in Moscow and at least 95 others on Saturday at demonstrations in cities across Russia against restrictions on freedom of assembly.
In St. Petersburg, Russia's second largest city, 60 of about 200 people were arrested in what Reuters witnesses said was one of the most violent recent crackdowns on protesters.
Reuters reporters said some of the detained had bloody noses while others had their heads beaten against police buses.
"Putin is the butcher of freedom," protesters in the northern city shouted as the detainees were taken away, directing their anger at Prime Minister Vladimir Putin.
Opposition activists traditionally stage demonstrations on the 31st day of those months that have 31 days to defend article 31 of the constitution, which guarantees the right to public gathering.
Activists say this gives them the right to hold protests without prior permission, which is regularly denied to opposition groups. Police habitually break up rallies not approved by the authorities.
In Moscow, along with Nemtsov -- a fierce critic of Russia's ruling elite -- the police arrested Left Front opposition leader Sergei Udaltsov and at least 35 others.
Mikhail Schneider, executive secretary of the Solidarity movement, told Reuters the protests were intended to promote democracy.
"We're here because the government has broken the constitution," he said. "Pay greater attention because people are lying to you about democracy in Russia."
'The demonstration doesn't interest me'
According to a recent poll by the Levada Centre polling service, only a quarter of Russians have heard of the Article 31 rallies.
On Saturday, Moscow's unsanctioned protesters disappeared in a crowd of several hundred people that gathered in Triumfalnaya Square in the city's center to watch a car and motorcycle show.
The crowd paid little attention to the demonstration.
"I'm here for the show, the demonstration doesn't interest me," said one young racing fan, declining to give his name.
The 82-year-old veteran human rights activists Lyudmila Alexeyeva said that the organizers will try next time to coordinate the protests with city hall.
"You see that such rallies now are stopped," she told journalists.
Earlier in Vladivostok about 30 people protested and no arrests were made.
"Our goal is to get from the authorities respect of the Article 31 of the constitution," Alexander Kurov, an activist with The Other Russia party in Vladivostok, said.
In the cities where the rallies took place activists chanted "Russia will be free," which by now has become a symbolic chant.