Police have briefly arrested Russian opposition leader Garry Kasparov at a banned anti-Kremlin rally in Moscow.
Mr Kasparov was one of about 170 people detained during a huge operation to prevent protesters from gathering at Pushkin Square. He has now been freed.
As he was being led away, the former chess champion said the Russian regime “is criminal, is a police state”.
President Vladimir Putin denies he is trampling on democracy, accusing the opposition of destabilising Russia.
Mr Kasparov leads the United Civil Front group, part of the opposition coalition The Other Russia.
He said he had been “walking with a group of people along the pavement without any slogans” when riot police had surrounded them.
“They grabbed everyone without distinction, without asking any questions,” he said.
Before being pushed away, he shouted: “Tell your leaders that this regime is criminal, is a police state. They arrest people everywhere because they are scared stiff.”
More than 9,000 police had been drafted into Moscow to prevent the rally going ahead.
Mr Kasparov’s swift arrest followed warnings by the prosecution office on the eve of the march, stating that anyone participating risked being detained.
And Mr Kasparov said the security presence meant the rally could not go ahead.
“I suppose it will be quite difficult to do anything now, you see, everything is shut off – there is a war-like situation in the city centre, as a matter of fact,” he told Russian radio.
The planned march came as Russia warned it wanted the extradition of London-based exile Boris Berezovsky.
Mr Berezovsky told the UK’s Guardian newspaper he was plotting “revolution” to overthrow Vladimir Putin.
Accusing Mr Putin of creating an authoritarian regime, the tycoon said that Russia’s leadership could only be removed by force.
Later, he clarified his words, stating that he backed “bloodless change” and did not support violence.
Other Russia has called for another massive march in St Petersburg on Sunday, which Moscow has also banned.