Opposition figures held in Moscow after rallies banned
Russian police have detained two opposition leaders and dozens of other activists trying to hold rallies in Moscow and St Petersburg.
Opposition groups were calling on the government to respect their right to peaceful assembly.
Reports say the crackdown in St Petersburg was particularly harsh, with some demonstrators injured.
In Moscow, the square where activists had planned to meet was sealed off for a rally-car and quad-bike display.
The means by which the authorities in Moscow prevent the opposition from even gathering for protests are becoming ever more bizarre, the BBC's Richard Galpin reports from Moscow.
Protesters brandished the number 31, after the article of the constitution guaranteeing the right to public gatherings. The date of the protests - 31 July - was symbolic.
'Anger and frustration'
Large numbers of riot police and troops from the ministry of the interior had been posted around the perimeter fence on the Moscow square, ready to pounce on the opposition activists as they arrived.
But a handful of opposition members did manage to mix into the small crowd watching the motor-show and then started shouting their slogans for freedom of assembly.
They were quickly tackled by the police who dragged them away.
Opposition figures Boris Nemtsov and Sergei Udaltsov were among those detained.
Among those watching in Moscow was Masha Lipman of the Carnegie Center in Moscow who said the police action showed how afraid the government was that the opposition movement might grow in strength.
"One more reason for concern on the part of the authorities is the economic crisis, is that there is discontent here and there, always small but there is less compliance overall," she told the BBC.
"There is no movement but there is a growing mood of anger, of discontent, of frustration."
Analysts also believe the government is becoming increasingly sensitive now because parliamentary and presidential elections are less than two years away.
Witnesses told Reuters news agency that the crackdown in St Petersburg, where the protesters included members of the extremist National Bolshevik group, was one of the most violent in recent years.
Reuters reporters said some of the estimated 60 people detained there had bloody noses while others had had their heads beaten against police buses. Photos on Russian websites show people with bloodied faces.