Russian President Vladimir Putin has defended his party's landslide election victory as a big personal endorsement, but foreign monitors said the poll was unfair and the West pressed for an inquiry.
Mr Putin, who ran as his party's top candidate in Sunday's vote, has vowed to use United Russia's victory to keep a hold over Russian politics after stepping down next year.
European states and the United States demanded Russia investigate claims of abuses while opposition parties said the vote had been marred by cheating to favour Mr
White House spokeswoman
Putin's party, which won 64.1 per cent of votes with most ballots counted.
But the Kremlin chief dismissed concerns, saying the United Russia party's victory was a "legitimate" vote of public trust.
"The choice has been made and I of course would like to address my special thanks to those who voted for United Russia," Mr Putin said.
"I headed the party list of this party and this is of course a sign of trust, including for United Russia."
United Russia, which will take a large majority of the 450-seat lower house of parliament, presented the vote as a referendum of support for the Kremlin chief, who must leave office next May after a March 2 nd presidential election.
Allegations of vote-rigging and fraud alarmed the European Union, which said free speech had been violated in the run-up to the vote, and the United States, which urged a probe.
Investors said the result was broadly positive but said they were waiting for any clues about the biggest question in Russian politics: who will Putin endorse in March elections and how the former KGB spy will preserve influence after stepping down.
Vladimir Putin
Mr Putin's party won nearly six times as many as the nearest challenger, the Communist party, whose leader said the vote was marred by "outrageous violations" and vowed to challenge the results in court. The Communists won 11.6 per cent of the vote.
The nationalist LDPR party and another pro-Kremlin party, headed by a Putin ally, took another 16 percent of the vote. Smaller free-market and liberal parties won no seats.
Russian officials were jubilant. "This is the result we were promised last Friday," said one government figure.
The concerns of foul play could tarnish relations between Russia and Western nations, which Mr Putin warned during the campaign to keep their "snotty noses" out of Russian affairs.
"Reports from Russia include that there were allegations of election day violations, and we have urged the Russians to look into those," White House spokeswoman Dana Perino said.
"It is vital that the Russian Central Election Commission urgently investigates all allegations of electoral abuses," Britain's foreign ministry said.
The German government said the results were "neither free, fair nor democratic". Britain said the fact that most Western monitors had been prevented from observing the vote was "deeply disappointing".
Observers from the Council of Europe and the Organisation for Security and Cooperation in Europe (OSCE) described the election as "not fair" in a statement, saying it "failed to meet many ... commitments and standards for democratic elections".
Europe's main ODIHR election watchdog decided not to monitor the election, citing obstruction by Russian authorities.
Opposition parties said one-sided press coverage, heavy use of government resources to campaign for pro-Kremlin parties, and irregularities in voting skewed the outcome.
The Communists, the liberal Union of Right Forces and opposition icon Garry Kasparov have all described the election, in separate comments, as the "dirtiest in Russian history".
Putin has been careful to give few clues about how power will be handed over to the victor of March elections, provoking intense speculation by investors who have invested billions of dollars since he was first elected in March 2000.
Opinion polls show Putin (55), a former KGB agent, is extremely popular after eight years in power. Voters credit him with restoring stability and national pride and like his tough nationalism and criticism of the West.