Russian police arrested more than 1,000 people as they gathered for a protest in Moscow on Saturday to demand free and fair elections, a monitor said, following a crackdown on the opposition.
The rally comes a week after the capital's biggest demonstration in years, when some 22,000 people protested the authorities' decision to block opposition candidates from standing for the city council in September.
Investigators raided the homes and headquarters of several disqualified candidates in the run-up to the fresh rally on Saturday.
Top Kremlin critic Alexei Navalny was jailed for 30 days for calling for the demonstration.
Other leading opposition figures and would-be candidates were also arrested in the hours leading up to the event, which comes amid declining living standards and a fall in President Vladimir Putin's approval ratings.
Police said a total of 1,074 people have been arrested for a variety of offences during an unauthorised demonstration in the centre of the capital.
More than 3,500 took part in the demonstration.
Local polls are a rare opportunity for dissenting voices to participate in political life as anti-Kremlin parties have been squeezed out of parliament over Mr Putin's two decades in charge.
Security was tight in central Moscow and police shut down the area outside city hall where protesters were planning to gather, forcing participants out onto side streets.
"This is our city!", "Shame!" and "We want free elections," the crowd chanted as police blocked off the site.
Politician and disqualified candidate Dmitry Gudkov was arrested shortly before the march. Earlier he had said the future of the country was at stake.
"If we lose now, elections will cease to exist as a political instrument," he said.
"What we're talking about is whether it's legal to participate in politics today in Russia, we're talking about the country we're going to live in."
While pro-Kremlin candidates enjoy the support of the state, independent candidates say they have been made to jump through countless hoops in order to get on the ballot for the city polls.
After activists and ordinary Muscovites staged pickets last week, including outside the local election commission building, investigators said they were launching a criminal probe into obstructing the work of election officials.
If found guilty, organisers risk up to five years in prison.
Navalny ally Ivan Zhdanov said he had been arrested shortly ahead of the demonstration. Barred candidate Ilya Yashin meanwhile announced he was detained in the early hours of Saturday morning following a raid on his home.
Would-be candidate Lyubov Sobol, who this week launched a hunger strike, was arrested at the demonstration.
Moscow Mayor Sergei Sobyanin had warned on social media beforehand that the authorities would act decisively to guarantee public order.
"According to information from law enforcement authorities, serious provocations are being prepared which pose a threat to the safety, lives and health of people," Mr Sobyanin had said in a statement.
"Attempts at ultimatums, disorder will not lead to anything good. Order in the city will be maintained."
Russia's Investigative Committee has already opened a criminal investigation into an opposition rally in June which it said may have obstructed the work of Moscow's electoral commission.
Police asked media to notify the authorities if they planned to cover the protest and urged Russians to skip the rally altogether.
Although the election to select members of Moscow city's parliament is not a national one, opposition activists view it as an opportunity to try to gain a foothold in the Russian capital where Kremlin-backed candidates have proved less popular in the past than in other parts of the country.
Mr Putin has been in power as either president or prime minister since 1999. He won a landslide re-election victory and a new six-year term in office last year, but has seen his popularity dip since then due to an unpopular pensions reform and five straight years of falling real incomes.