MOSCOW -- Several thousand people turned out on a cold and rainy night to protest what observers and opposition leaders say were rigged parliamentary elections that gave a fraudulent victory to Prime Minister Vladimir Putin and his ruling United Russia party.
As an icy rain fell, an initial crowd of hundreds who gathered on a tree-lined boulevard for a sanctioned rally swelled to as many as 10,000, as chants of "Putin out!" and "Russia without Putin!" rang out.
The protest is thought to be the largest Russian opposition rally in years.
Reports suggested police arrested around 300 protesters in Moscow.
A similar demonstration in Russia's second city of St. Petersburg resulted in around 100 arrests.
Domestic And International Criticism
Widespread displeasure with Putin and his party has surrounded the December 4 poll, which the Organization for Security and Cooperation in Europe (OSCE) said exhibited "limited political competition and a lack of fairness."
The independent Golos election watchdog organization also said that it had received more than 1,500 complaints of electoral violations and was the subject of targeted harassment from government authorities.
President Dmitry Medvedev has said the reduced showing for United Russia as "no tragedy" and painted the result as a victory for Russians.
Opposition leader Vladimir Ryzhkov, who spoke at the Moscow protest rally, said the official results could not be considered legitimate.
"About 10 to 15 percent of the votes were the result of ballot box stuffing, falsifications, and the rewriting of protocols. United Russia's real result is no more than 35 percent, maybe even less than that," he said.
"They have the most catastrophic situation in cities with a population of over 1 million: They got 20 to 25 percent there, at best. So, this is a failure," Ryzhkov added.
Even with the claims of fraud, the more than 49 percent of the vote United Russia is said to have won represents a significant drop from the last election, when it claimed 64 percent of the vote.
This year, three parties split the remaining vote: the Communist Party, A Just Russia, and the Liberal Democratic Party.
In the United States, White House spokesman Jay Carney expressed "serious concerns."
"We have serious concerns about the conduct of those December 4 parliamentary elections," Carney said. "These concerns are reflected in the preliminary report issued by the OSCE's election observation mission, including a lack of fairness in the process, attempts to stuff ballot boxes and the manipulation of voter lists, among other things."
Carney said Washington was "equally" concerned with "reports that independent Russian election observation efforts including the nationwide Golos network and independent media outlets encountered harassment of their personnel and cyberattacks on their websites."
"We applaud the initiative that these and many other Russian citizens have taken to participate constructively, a positive development that the OSCE report also highlighted," Carney said.
Our correspondent reported seeing several thousand protesters crowded onto the boulevard that stretches away from Moscow's Chistye Prudy metro, with some people climbing fences to better hear the speakers. Among those who rallied the crowd were the anticorruption blogger Aleksei Navalny, writer and liberal Dmitry Bykov, Yevgenia Chirikova from the Save Khimki Forest movement, opposition leader Boris Nemtsov, and Solidarity Youth head Ilya Yashin.
WATCH: Raw video footage with natural sound of the protests and confrontations with police in the Russian capital late on December 5:
Nemtsov called the election "a crushing defeat for Putin and his party of swindlers and thieves," and said there have been 'thousands [of reports] of falsification facts, of 'carousel' voting, [and] stuffed ballot boxes."
"We're now starting a campaign to open a criminal case against these vermin. They stole 13 million votes from us. In Moscow they didn't even get 25 percent but drew up 46 percent for themselves," he said. "Our observers across the whole country traced total violations. So [United Russia leaders] can conduct themselves however they like, but no one believes them at all."
Among the Moscow protesters was Anna, a 22-year-old student, who told RFE/RL, "We came here because the results that they have given us are an insult and it's an insult to us that our vote didn't play a role."
"We decided to come here because we observed how things happened [on December 4] and last night, we watched all the videos on YouTube showing all this falsification and ballot stuffing. We've seen that there are pens at polling booths that have disappearing ink in them and all these things," he said. "We asked our friends, our relatives, and their friends who they voted for and none of them said United Russia. And still we get this fantastical result. We came here today to support people like us who don't agree with this result."
Police Clamp Down
Police in riot gear eventually detained some 300 people in the capital, reports said.
At one point, hundreds of people who had begun marching toward the Central Elections Commission were stopped and taken away in buses.
Our correspondent reported seeing dozens of police buses and riot police in helmets and batons forcing apart protesters who had interlocked their arms.
Amnesty International issued a statement criticizing what it said were at least 300 arrests made over the weekend and calling on authorities to release everyone in custody.
Nicola Duckworth, director of Amnesty International's Europe and Central Asia Program, said, "These disgraceful detentions highlight once again the failure of the Russian government to respect its citizens' rights to freedom of expression and assembly."
The election and protests come just three months before Russia votes for a new president, with Putin still the odds-on favorite to win.
Tom Balmforth reported from Moscow, with additional reporting from RFE/RL's Russian Service and agency reports