Yesterday hundreds of people were arrested in Moscow for staging an anti-Kremlin rally, with opposition politician Garry Kasparov among them.
The former chess grandmaster is now leader of the United Civil Front Group, which is a constituent part of opposition alliance Other Russia that organised this weekend's demonstrations in protest at president Vladimir Putin's regime.
Protestors at today's rally in St Petersburg said that the streets were lined with thousands of riot police and interior ministry troops armed with water cannons.
Olga Kurnosova, the leader of Mr Kasparov's United Civil Front in St Petersburg, said that she had been detained by police as soon as she left her house this morning.
"They have also detained dozens of others at the train station and on their way to the rally," she told the Reuters news agency.
But Ms Kurnosova predicted that the authorities' actions could be playing into activists' hands.
She explained: "After what Moscow and Russian authorities are doing, I think far more people will come."
Other Russia insists that its demonstrations are an entirely peaceful protest against Mr Putin's running of the country, but the Kremlin has accused the coalition of seeking to destabilise the president's rule ahead of his second and final term ending in 2008.
Authorities had used comments by billionaire exile Boris Berezovsky last week as a pretext for claims the demonstrations were aimed at usurping Mr Putin.
London-based Mr Berezovsky told the Guardian newspaper on Friday that he was putting together a "revolution" to overthrow the Russian president, although he has since clarified his remarks by stating he is seeking "bloodless change".
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