Police locked down the centre of Moscow and other cities on Sunday as protesters took to the streets across Russia demanding the release of jailed Kremlin critic Alexei Navalny.
Hundreds of police in riot gear lined the streets of the capital from the early hours of Sunday morning, restricting movements of pedestrians around the centre.
In a rare move, Moscow city authorities also closed several central Metro stations and diverted overground transport.
Opposition supporters had called for a second weekend of demonstrations after tens of thousands protested across the country last Saturday over the arrest of President Vladimir Putin's most prominent opponent.
With protests beginning in Moscow and Saint Petersburg, independent monitor OVD-Info said at least 650 people had so far been detained across the country. It reported more than 4,000 detentions during last weekend's protests.
Navalny was detained at Moscow airport in mid-January after flying back to Russia from Germany where he was recovering from an August poisoning he blames on the Kremlin.
The 44-year-old anti-corruption campaigner is being held in a Moscow detention centre and facing years of potential jail time in several different criminal cases, despite calls from Western governments for his release.
- 'People are outraged' -
On Sunday protesters rallied in cities including Vladivostok in the Far East, where several dozen gathered in a central square despite police closing it off ahead of the rally.
Several thousand were also reported to have protested in the Siberian city of Novosibirsk despite temperatures dropping to -20 degrees Celsius (-4 degrees Fahrenheit).
Local politician and Navalny ally Helga Pirogova told AFP that Sunday's protest in Novosibirsk was potentially bigger than the week before.
"People are still outraged by what is happening," the 32-year-old said.
In Moscow organisers were scrambling to deal with the massive police effort, announcing last-minute changes in locations as AFP journalists saw police starting to detain people.
Hundreds were marching through the centre chanting "Freedom!" and "Putin is a thief!"
In second city Saint Petersburg police closed off the main thoroughfare Nevsky Prospekt and police cars were parked all across the centre, an AFP journalist reported.
"The whole centre is cordoned off," said Natalya Grigoryeva, who came to the Saint Petersburg rally with her daughter. "And who is this all against, against their own people?"
Russian authorities have issued several warnings against participating in the unauthorised rallies and threatened criminal charges against protesters.
Navalny is due in court in several cases next week, including on February 2 on charges of violating the terms of a 2014 suspended sentence.
His wife Yulia posted a picture of her family on Instagram on Sunday, urging supporters to make their voices heard.
"If we remain silent, then tomorrow they will come for any one of us," she wrote.
- Allies in custody -
This week several Navalny associates, including lawyer Lyubov Sobol and his brother Oleg, were placed under house arrest until late March pending charges for violating coronavirus restrictions by calling people to join protests.
Navalny's spokeswoman Kira Yarmysh was detained late Saturday also over violating virus measures, the same day she was due to walk free after a nine-day jail term for violating protest laws.
The head of Navalny's Anti-Corruption Foundation, Ivan Zhdanov, said Saturday the Investigative Committee informed him that a criminal case on fraud charges had been launched against Navalny.
In December last year, investigators said they were initiating a probe into Navalny allegedly misappropriating over $4 million of donations to his organisations.
Days after Navalny was taken into custody, his team released a video report alleging Putin had been gifted a $1.35 billion property on the Black Sea coast, garnering over 100 million views on YouTube.
The Kremlin has denied that the Russian president owns the opulent complex, which according to Navalny features an underground ice hockey arena, a private casino and vineyards.
Billionaire businessman Arkady Rotenberg -- Putin's former judo partner who is under Western sanctions -- said Saturday he was the owner of the property and that he was building a hotel there.