Baton-wielding riot police have broken up anti-corruption protests and detained hundreds of demonstrators in Moscow and other Russian cities while a court has sentenced opposition leader Alexei Navalny to his second prison term this year.
The protests on Monday, called by Mr Navalny, a strong critic of Russian President Vladimir Putin, drew thousands of people and were some of the biggest in Russia since 2012.
"Russia without Putin" and "Russia will be free" chanted the demonstrators, including many young people, who crowded into central Moscow on a public holiday.
Mr Navalny, who is mounting a long-shot bid to unseat Putin in an election next year, had called for mass protests in Moscow and other cities against official corruption.
The Kremlin has dismissed Mr Navalny's graft allegations, accusing him of irresponsibly trying to whip up unrest.
The scale of the protests in Moscow and smaller ones in St Petersburg and scores of other cities suggests Mr Navalny has maintained his campaign's momentum despite more than 1000 people being arrested after the last such protest in March.
That is likely to embolden him to call for more protests and keep Putin, who is expected to run for and win re-election next year, under rare domestic pressure.
"Neither mass detentions nor criminal cases after March 26 (the last protest) worked," wrote Lyubov Sobol, a Navalny ally, on social media. "People are not afraid."
The OVD-Info monitoring group, a non-profit organisation, said preliminary figures showed 730 people had been detained in Moscow. The Interior Ministry said 500 people were detained in St Petersburg.
Mr Navalny's wife, Yulia, said her husband was detained as he tried to leave their home. Reuters witnesses saw a police car leaving his apartment compound at high speed, followed a few minutes later by a minibus carrying about 10 policemen.
Electricity in his office was cut at around the same time as he was detained, briefly bringing down a live feed of the protests, Mr Navalny's spokeswoman said.
At a midnight court hearing, a Russian judge later found Mr Navalny guilty of repeatedly violating the law on organising public meetings and sentenced him to 30 days in prison.
He served a 15-day jail term after the protest in March.