Foreign observers have said that Russia's parliamentary election, won by President Vladimir Putin's party, was "not fair".
More than 60% of the voters cast their ballots, officials say
The statement was made by a joint observer team of the Organisation for Security and Co-operation in Europe (OSCE) and the Council of Europe.
With nearly all ballots counted, Mr Putin's United Russia had 64.1% of the vote, the electoral commission said.
Mr Putin said the poll was "legitimate" and a vote of public trust in him.
The election "was not fair and failed to meet many OSCE and Council of Europe commitments and standards for democratic elections," the observers from the OSCE's Parliamentary Assembly and the Council of Europe's Parliamentary Assembly told a news conference in Moscow.
The statement criticised "abuse of administrative resources" and "media coverage strongly in favour of the ruling party".
The polls "took place in an atmosphere which seriously limited political competition" and "there was not a level political playing field", it said.
The OSCE had sent 330 foreign monitors to cover nearly 100,000 polling stations - far fewer than it had originally planned. It has accused Moscow of imposing curbs and delaying monitors' visas. Russia has denied the claims.
Russia's electoral commission has dismissed mounting criticism from opposition activists and international governments, saying there were no serious violations on election day.
Kremlin spokesman Dmitry Peskov said the vote was "free and fair".
The Communist Party, which with 11.6% of the vote was the only opposition party to gain seats in the State Duma, said it would mount a legal challenge to the result and would decide whether to boycott the new parliament.
The prominent opposition activist and former chess world champion Garry Kasparov described the election as "the most unfair and dirtiest in the whole history of modern Russia".
Several Western governments also expressed concern over the reports of irregularities.
"Russia was no democracy and it is no democracy," said German government spokesman Thomas Steg.
The US, Britain and France have called on Russia to investigate the alleged violations in the poll.
Nato Secretary General Jaap de Hoop Scheffer also expressed concern over the conduct of the elections.
With 98% of the vote counted, the country's liberal opposition parties looked certain to fail to clear the 7% threshold needed to enter parliament.
In total, 11 parties were competing for places in the 450-member lower chamber of the State Duma.
Two parties allied to the Kremlin - A Fair Russia and the right-wing Liberal Democratic Party - were poised to win seats.
Mr Putin described the election as a "good example of domestic political stability" and thanked the voters for the turnout of 63%.
"This feeling of responsibility of our citizens is the most important indication that our country is strengthening, not only economically and socially but also politically," Mr Putin said.
The independent Russian monitoring group, Golos, had earlier reported various violations during the voting, which it said amounted to "an organised campaign".
It had claimed that in a number of cases state employees and students were pressured to vote, and those voting for United Russia were entered into a prize lottery in St Petersburg.
In Russia's troubled region of Chechnya, run by pro-Kremlin President Ramzan Kadyrov, electoral officials have said a partial count showed United Russia won more than 99% of the votes on a 99% turnout.
United Russia's leader Boris Gryzlov acknowledged there had been violations but dismissed them as insignificant.
On Monday, some 10,000 members of the pro-Putin Nashi (Ours) youth group held a rally in Moscow to celebrate United Russia's victory.
Mr Putin is constitutionally obliged to stand down after his second term as president ends in March next year.
Mr Putin's next steps will be keenly watched at home and abroad
The BBC's James Rodgers in Moscow says his party's win will enable him to continue wielding great influence in politics - even if he is no longer in high office.
Mr Putin announced this year he may seek the office of prime minister after his presidential term ends.
If predictions are correct and the Liberal Democratic Party enters parliament, its candidate Andrei Lugovoi - who is wanted in the UK for the murder of former Russian spy Alexander Litvinenko - will be guaranteed a seat.
A parliamentary seat would grant him immunity from prosecution and extradition.