President Vladimir Putin's party scored a landslide win in Russia's election, results showed on Monday, but the opposition vowed to challenge an outcome that could help Putin keep a grip on power after he leaves office.
In the first foreign reaction, the White House urged Russia to investigate opposition claims of widespread ballot-rigging in the vote which, according to incomplete official results, gave Putin's United Russia party more than 60 per cent of the vote.
The Kremlin hailed the result as a signal from Russian voters that they want Putin -- required by the constitution to step down when his second term ends next year -- to retain influence even after he leaves office.
"Russian voters spoke in favour of United Russia, thus supporting President Putin's course, and spoke in favour of it being continued after the current president's second term ends," Dmitry Peskov, a Kremlin spokesman, told Reuters.
But the Communists, likely to be the only opposition force in parliament, said they would challenge the result in the Supreme Court. They said they would meet later on Monday to decide whether to boycott the new parliament.
Liberal Kremlin critic Boris Nemtsov of the SPS party called Sunday's vote "the most dishonest election in the history of modern Russia."
With 79.4 per cent of votes counted, United Russia had 63.3 per cent of the vote and the Communists 11.7 per cent. Only two other parties -- Fair Russia and LDPR which both back the Kremlin -- cleared the 7-per cent hurdle to qualify for seats.
The 55-year-old Putin, a former KGB spy who is hugely popular and credited by voters with restoring Russia's national pride, has been tipped for a role as prime minister or possibly speaker of parliament after his presidency.
Some observers say he could seek a third term as president, though he has said repeatedly he would not change the constitution to pave the way for this.
Allegations of ballot fraud are unlikely to strike a chord with the majority of Russians who, opinion polls show, respect Putin and want him to stay on as a "national leader." The opposition parties most critical of Putin have marginal support.
"I voted for United Russia because I believe that Putin can help us, simple working folk," said Sergei Ilin, 34, an unemployed man in the Siberian village of Belovsky.
But the allegations could drive a new wedge between an increasingly assertive Moscow and the West which Putin accused last week of "poking their snotty noses" in Russia's affairs.
White House National Security Council spokesman Gordon Johndroe noted the allegations of violations and said: "We urge Russian authorities to investigate these claims."
Europe's main ODIHR election watchdog -- seen in the West as a key yardstick of the fairness of an election -- pulled out of the vote citing obstruction by the Russian authorities.
The head of Russia's Central Election Commission, Vladimir Churov, a former colleague of Putin who was appointed election chief this year, dismissed allegations of fraud. "I think there were no serious violations on polling day," Churov said.
Chris Weafer, chief strategist at Uralsib investment bank in Moscow, said the results were "not spectacular but good enough to allow President Putin to call the shots after (the presidential election in) March."
"He now has the initiative in terms of what role he wants to stay on in", said Weafer.
In Chechnya, scene of a separatist insurgency and now under the autocratic rule of pro-Putin leader Ramzan Kadyrov, United Russia won 99.4 per cent of the vote -- a new record for Russian parliamentary votes, election officials said.
Russians credit Putin with overseeing an oil-fuelled economic boom and like his no-nonsense approach, even while many in the West see it as squashing democratic freedoms.
But independent election monitors and opposition parties said officials mounted a nationwide campaign of bribery, intimidation and ballot-stuffing to make sure the vote handed Putin a resounding mandate.
The allegations included voters being offered the chance to win televisions and refrigerators if they backed Putin, and a report people were being bussed around the city of St Petersburg and voting in one polling station after another.
"These are not isolated incidents. The complaints are from every corner of Russia," said Grigory Melkonyans of Golos, Russia's biggest independent election observer.
The result means Andrei Lugovoy, Britain's chief suspect in the radiation poisoning murder of Kremlin critic Alexander Litvinenko, is set to become a member of parliament. He was No. 2 on the LDPR's slate of candidates. Lugovoy denies any guilt.
Litvinenko's widow Marina said in a statement her reaction to the election was "something between disgust and sadness."