United Russia, backed by President Vladimir Putin, has won a majority in the country's parliamentary election, far ahead of rival parties.
With 93% of the votes counted, the party has secured 54.2% of ballots and 343 seats in the 450-member parliament, officials say.
Mr Putin said his party had "achieved a very good result", however the turnout was a record low of 47.8%.
The Communist Party and nationalist LDPR both secured just over 13%.
The party A Just Russia gained just over 6% of the votes. All four parties are loyal to Mr Putin and dominated the last parliament, or State Duma.
Mr Putin has enjoyed 17 years in power as either president or prime minister.
Voting irregularities were reported in several areas and the head of the election commission suggested that the results might be cancelled in three polling stations.
Liberal opposition parties failed to get enough votes for party-list representation. "To my utmost regret, not one other party managed to get over the 5% barrier," said Central Election Commission head Ella Pamfilova.
The two main opposition parties allowed to field candidates, Yabloko and Parnas, received just 1.89% and 0.7% respectively.
Half the seats were also being contested in constituencies but even there the small number of opposition candidates failed to win.
The result increases United Russia's majority, after it achieved 49% of the vote in the 2011 Duma elections. The party, led by Prime Minister Dmitry Medvedev, will take more seats in parliament, up from 238.
However, the turnout, based on partial figures, was the lowest in Russia's modern history and significantly down on the 60% turnout in 2011.
Election commission head Ella Pamfilova - a respected human rights activist - said she was "fully confident that the elections are proceeding in a quite legitimate way". But later she warned that results at three polling stations might be cancelled because of irregularities.
There were reports of serious irregularities in one Siberian region, with suggestions of "carousel" voting - people bussed around polling stations - in the city of Barnaul.
In the Caucasus, youths smashed up a polling station in the Khunzakh district of Dagestan, accusing officials of stuffing ballots to favour one candidate, Ms Pamfilova said.
And in the southern region of Rostov a criminal case was opened for alleged electoral fraud, she said.
Some voters unhappy with the election posted pictures of their spoiled ballots on Twitter and Instagram. Some of them mockingly voted for "Pikachu" - fictional creatures from the hugely popular Pokemon Go game.
Chechen leader gets 98%
For the first time, people voted in Crimea, annexed from Ukraine in 2014 in a move condemned internationally. United Russia won all the region's constituency seats, in a vote that prompted protests in the Ukrainian capital, Kiev.
Chechnya's leader Ramzan Kadyrov - a firm ally of Mr Putin who runs his troubled North Caucasus republic with an iron fist - swept to victory with 98% support, with 78% of votes counted.
Vote-rigging sparked big anti-government street protests after Russia's last parliamentary election in 2011.
In the system of "managed democracy" crafted by the Kremlin, it was unthinkable that President Putin's control of parliament would weaken, the BBC's Steve Rosenberg reports from Moscow.
Mr Putin will be hoping that this time his personal popularity, combined with widespread apathy, will mean that Russians accept the result, he says.
The independent election monitoring group Golos said that "although the level of violations in this election campaign was lower than in 2011 there were many in the run-up to the voting".
It said the elections were "far from what could be called really free and fair". The number of independent observers at polling stations was lower than before, and there were cases of ballot-stuffing, carousel voting and other abuses, Golos complained.
'Party of power in power again' - media reaction
Russian papers see the result largely as a vote of confidence in President Putin - and as pretty much predictable.
"The election is primarily an informal referendum on trust in the person who is in charge of making all the key decisions," tabloid Moskovsky Komsomolets declares.
Russian state Rossiya 24 TV mentioned allegations of election fraud, but said they were not significant and were being investigated.
But business daily Vedomosti says that - despite the authorities' promises - the election "was not a model of honesty".
Source: BBC Monitoring
After the vote Mr Putin visited the headquarters of United Russia with Mr Medvedev to congratulate activists on their victory.
"We know that life is hard for people, there are lots of problems, lots of unresolved problems," Mr Putin said. "Nevertheless, we have this result."
Despite Russia's economic malaise and tensions with the West over the conflicts in Ukraine and Syria, the poor turnout reflected widespread apathy among voters.