Opposition politicians and election monitors have alleged extensive elections violations during voting in Russia's parliamentary polls, as preliminary tallies indicate a decline from 315 to 220 in the ruling party's seats.
United Russia took 48.5 per cent of the votes, down from 64 per cent in 2007. And the Communists came in second with around 20 per cent.
Several parties on Sunday complained of irregularities aimed at boosting United Russia's vote count, including intimidation of voters.
In Vladivostok in the east, voters complained to police that United Russia was offering free food in exchange for promises to vote for the party.
Turnout was low in many areas was lower Sunday compared to the previous election.
The vote is seen as an important test of Prime Minister Vladimir Putin's popularity, just three months before he is due to stand in presidential elections.
His United Russia party is expected to win Sunday's polls but could lose its constitutional majority and end up having to share power in parliament with their political rivals.
Only seven parties have been allowed to field candidates for parliament this year, while the most vocal opposition groups have been denied registration and barred from campaigning.
Al Jazeera's Neave Barker, reporting from Moscow, said: "The country's only independent election observer called Golos reported that more than 5,000 irregularities have been recorded, many of them connected with people pressured to vote mainly for the country's biggest and most powerful party, United Russia".
"There have been some skirmishes today in and around Red Square," our correspondent said. "The capital is on lockdown, and the police are looking for any sign of trouble, with more protests expected later on."
Speaking to Al Jazeera, Garry Kasparov, a political activist and former world chess champion, said: "All the other parties participating in this so called election are 100 per cent under the Kremlin's control.
"Voting for them is to vote for puppets in the theatre of the absurd."
About 30 opposition protesters gathered by the Kremlin screaming: "Your elections are a farce!" through loudspeakers. Twelve were detained by police, Reuters witnesses said.
Communist Party leader Gennady Zyuganov said his party monitors thwarted an attempt to stuff a ballot box at a Moscow polling station where they found 300 ballots already in the box before the start of the vote.
He said incidents of ballot-stuffing were reported at several other stations in Moscow, Rostov-on-Don and other areas. In the southern city of Krasnodar, unidentified people posing as Communist monitors had shown up at polling stations and the real observers from the party were not allowed in, Zyuganov said.
Golos, the country's only independent election-monitoring group, and two liberal media outlets said their sites had been shut down by hackers intent on silencing allegations of violations.
Golos said its "Map of Violations" website documenting reports of
fraud was inaccessible due a cyber-attack and its email was paralysed.
Golos also said it was excluded from several polling booths in the Siberian Tomsk region.
Many election violations involved absentee ballots, Golos director Liliya Shibanova said. People with absentee certificates were being bused to cast ballots at multiple polling stations, he said.
Moscow prosecutors launched an investigation last week into Golos' activities after legislators objected to its Western financing.
Russian customs officers held the director of Golos for 12 hours at a Moscow airport on Saturday, seizing her laptop computer in what the group said was an attempt to stop it monitoring the election.
Mikhail Kasyanov, a former prime minister during Putin's first presidential term, said he and other opposition activists who voted were under no illusion that their votes would be counted fairly.
"It is absolutely clear there will be no real count," he said. "The authorities created an imitation of a very important institution whose name is free election, that is not free and is not elections."
Russians voted across nine time zones across the 9,000km-wide country, with the first voters in far eastern regions going to the polls at 20:00 GMT on Saturday and voting stations closing at 17:00 GMT on Sunday in the enclave of Kaliningrad, wedged between Poland and Lithuania.