Western nations have urged Russia to probe charges of fraud during weekend elections that gave President Vladimir Putin's party a landslide victory.
Germany has blasted the country as undemocratic.
“There can be no doubt that, measured by our standards, these were not free and fair elections, they were not democratic elections,” German government spokesman Thomas Steg told reporters.
“Russia was no democracy and it is no democracy,” Mr Steg added.
He said Moscow must “thoroughly and transparently” probe complaints that the election was weighted in favour of Mr Putin's United Russia party and move towards a true multi-party system.
Washington has urged Russia to investigate “allegations of election day violations”. Britain, France and Italy followed suit, but stopped short of Germany's outright condemnation of the poll as flawed.
“It is vital that the Russian Central Election Commission urgently investigates all allegations of electoral abuses,” a British Foreign Office spokesman said.
“The government is concerned about allegations of electoral malpractice which, if proven correct, would suggest that the Russian elections were neither free nor fair.”
Italian Prime Minister Romano Prodi said it was in the Russian authorities' interest to “clarify” the poll's outcome and put the concerns of the international community to rest.
Paris called on Moscow to probe the allegations of foul play, which included liberal opposition campaigner and former world chess champion Garry Kasparov calling the vote “the dirtiest” in Russian history.
“We hope the Russian authorities will be able to shed full light on these allegations,” French foreign ministry spokeswoman Pascale Andreani said.
'Chronicle of a victory foretold'
According to the Kremlin, however, French President Nicolas Sarkozy “warmly congratulated” Mr Putin on his party's victory in a telephone call to the Russian leader.
The White House said US President George W. Bush had no plans to telephone Mr Putin but that Washington would issue further reaction to the vote.
Austria condemned the election result as “chronicle of a victory foretold”.
The European Commission reserved judgement on the poll until it has studied “reports from different sources” while NATO chief Jaap de Hoop Scheffer voicing concern over democratic freedoms in Russia.
The Organisation for Security and Cooperation in Europe (OSCE) said the ballot had fallen far short of international standards.
Goran Lennmarker, the head of the OSCE's Parliamentary Assembly, told reporters in Moscow: “These elections failed to meet many of the commitments and standards we have in the OSCE and Council of Europe.”
He highlighted the strong links between the state and United Russia, which ran a campaign that overwhelmed all its rivals, and said this amounted to “an abuse of power”.
With 98 percent of ballots counted, Mr Putin's party had secured 64.1 percent of the vote, giving it more than two-thirds of seats in the State Duma – a majority sufficient to change the constitution.
Berlin urged Mr Putin not to tamper with the constitution — which bars him from seeking a third presidential term — saying it would put at risk Russia's reputation.
The Baltic States — former Soviet-occupied Lithuania, Latvia and Estonia — and the Czech Republic all accused Russia of ducking democracy in Sunday's poll, but Poland said it would not question the outcome.
Polish Prime Minister Donald Tusk said indications of shortcomings were “worrying” but added “this is nonetheless the Russians' choice and I don't see a reason to call that into question.”
Finland too signalled it would accept the result, with Prime Minister Matti Vanhanen saying the outcome clearly reflected United Russia's popularity.
Lithuanian President Valdas Adamkus said he was not surprised by Putin's party's resounding victory.
“Nor is the rest of the world …I can only regret that Russia did not opt for democratic principles and did not move forward.”
Estonian Foreign Minister Urmas Paet said he hoped there would still be parliamentary elections in Russia in future. “That way, the opportunity will always be there for them to become free and democratic.”