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 percent 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."
