In recent weeks, thousands have attended street protests calling for free and fair elections after the exclusion of several opposition figures from local Moscow polls next month.
Tens of thousands of opposition supporters rallied in Moscow on Saturday after mass police detentions at recent protests that have been among the largest since President Vladimir Putin's return to the Kremlin in 2012.
On a cold rainy afternoon, protesters huddled under umbrellas on the central Prospekt Andreya Sakharova street, where city authorities had given permission for the rally to take place but deployed a massive police presence, including officers in riot gear.
The White Counter, an NGO that tracks participants in rallies, counted 40,000 people, while Moscow police gave a much lower attendance figure of 20,000.
In recent weeks, thousands have attended street protests calling for free and fair elections after the exclusion of several opposition figures, including allies of top Putin critic Alexei Navalny, from local Moscow polls next month.
Riot police and the national guard detained more than 2,000 at the previous two rallies, which were not authorised by city officials.
'Feels like country is a prisoner'
On Saturday, some protesters carried placards with slogans such as "Give us the right to vote!" and "You've lied to us enough" while others held up pictures of activists arrested at earlier demonstrations.
"I'm outraged by this injustice at every level. They're not letting candidates stand who have collected all the necessary signatures. They are arresting people who are protesting peacefully," said one protester, Irina Dargolts, a 60-year-old engineer.
"It feels like the country is a prisoner and its citizens are hostages...No one represents the people," said Dmitry Khobbotovsky, an activist for the Open Russia movement funded by Kremlin foe and former oligarch Mikhail Khodorkovsky.
Most opposition candidates who have been banned from participating in the vote have been jailed for violating protest laws.
One of the speakers at the rally was the wife of opposition politician Dmitry Gudkov, who is serving a 30-day sentence.
"Each of us has the right to run for office and they are very afraid of that," said Valeriya Gudkova.
"We have real support from the public and they just have criminals in their electoral commissions."
A dozen protesters including university students face criminal charges of "mass disorder" that risk lengthy prison terms, despite their supporters insisting the protests were peaceful.
Saturday's rally was authorised, meaning participants should not face detention. But Navalny, who is currently in jail, urged supporters to walk peacefully through the city afterwards when they will risk detention for illegal protests.
"After the demonstration, we're going for a walk around Moscow," his team wrote on social media on Saturday.
Moscow police and the powerful Investigative Committee issued a warning against participating in unsanctioned protests which it said would be "immediately halted."