Russian police arrested dozens of people as they gathered at Moscow city hall Saturday to demand free and fair elections, an AFP journalist said, following a crackdown on the opposition.
Thousands of Russians had vowed to take to the streets of the capital after authorities refused to allow opposition and independent candidates to stand for Moscow's city council in September.
Investigators raided the homes and headquarters of several disqualified candidates in the run-up to the protest, while top Kremlin critic Alexei Navalny was jailed for 30 days for calling for the demonstration.
Other leading opposition figures and would-be candidates were arrested in the hours leading up to the event.
The Saturday protest is the latest in a series of rallies over the local election, which comes amid declining living standards and a fall in President Vladimir Putin's approval ratings.
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 Putin's 20 years in power.
Security was tight in central Moscow on Saturday and an AFP journalist said at least 50 people had been arrested before the planned start of the demonstration at two pm local time (1100 GMT).
Protest monitoring organisations reported dozens more arrests.
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."
Elena Rastovka, a 68-year-old pensioner at the demonstration, told AFP: "I've been afraid all my life, but enough is enough. If we stay at home nothing will change.
"Authorities arrest people who want to challenge them. Look at what they're doing -- the authorities do not like the people."
Navalny ally Ivan Zhdanov said he had been arrested shortly ahead of the demonstration, while barred candidate Ilya Yashin announced he was detained in the early hours of Saturday morning following a raid on his home.
- 'Security threat' -
Moscow Mayor Sergei Sobaynin called the unauthorised protest a "security threat", adding that "order will be ensured according to the relevant laws".
Last weekend 22,000 people turned up for a protest in Moscow, the largest such demonstration in years, after election authorities refused to register dozens of candidates.
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.
Rejected candidate Lyubov Sobol this week launched a hunger strike in protest.
On Thursday, the 31-year-old demanded officials review her documents and came to the offices of the Moscow election commission to continue her strike.
But security agents took her out of the building on the sofa she was sitting on.
After activists and ordinary Muscovites staged pickets, 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.
- ' Impossible not to protest' -
Nearly 11,000 people indicated interest in the rally on Facebook.
Police asked media to notify the authorities if they planned to cover the protest and urged Russians to skip the rally altogether.
Viktoria Popova, a 30-year-old illustrator, said she could not miss it.
"It is impossible not to come, it's impossible to feel powerless, unable to change anything," she told AFP.
"Who would have thought it would become important to take part in such a bizarre and boring affair as the Moscow parliament election?"