Russian riot police beat opposition activists yesterday and detained nearly 200 people at protest rallies against President Vladimir Putin in St Petersburg, Russia's second city.
Riot police also detained Boris Nemtsov and Nikita Belykh, leaders of the Union of Right Forces (SPS) party who are both running in a December 2 parliamentary election. They were later released.
Witnesses saw riot police beating activists with batons and their fists before forcing them into police buses.
Dozens more were detained outside the Winter Palace, the residence of the Tsars, and at another rally in central St Petersburg, Vladimir Putin's home town.
"They have forbidden us from discussing Putin," Mr Nemtsov told the crowd. "But we have come here today to ask Mr Putin and the authorities why is there so much corruption in the country?"
He was promptly detained by five riot policemen as the crowd chanted "Russia without Putin".
Mr Nemtsov said his detention was a breach of Russian law which forbids police from detaining candidates.
"Putin has total disregard for the country's Constitution and laws," Mr Nemtsov said. "He is afraid the people will find out the truth and so he hides behind the riot police."
About 500 activists made it to the marches but were vastly outnumbered by riot police. Most of those detained were later released, organisers said.
The city authorities had not given permission for the march and streets in the city centre were blocked by riot police and snow-clearing trucks.
The "march of the discontented" brings together Mr Putin's opponents into one movement which includes Other Russia, free-market parties such as SPS and Yabloko as well as anarchists and radical socialists.
Police on Saturday detained other Russia leader and former world chess champion Garry Kasparov when they broke up a march of about 3,000 in Moscow. Activists said 60 people were detained at that march.
Vladimir Putin's opponents accuse the Kremlin chief of cracking down on the freedoms won after the 1991 fall of the Soviet Union and of creating what they say is an unstable political system dependent on Mr Putin alone.