Alexey Nikolsky / EPA
The United Russia party of President Dmitry Medvedev, left, and Prime Minister Vladimir Putin suffered a setback in Sunday's election.
Reuters reports that Russian Prime Minister Vladimir Putin's ruling party lost 77 seats in parliament in an election held on Sunday, according to projections made by the Central Election Commission based on preliminary results. Putin's United Russia is expected to end up with 238 seats, a slim majority in the 450-member lower house. The party previously held a two-thirds majority allowing it to change the constitution without opposition support.
The Communist Party made substantial gains.
Opposition parties say the election was unfair from the start because of authorities' support for United Russia with cash, influence and television air time. European monitors also said Monday the vote was marred by apparent manipulations including ballot box stuffing.
Updated at 9:50 a.m. ET: Secretary of State Hillary Clinton said she had "serious concerns" about the conduct of Russia's parliamentary elections. Speaking on the sidelines of an international conference on Afghanistan, Clinton told reporters that Russians deserved a full investigation of all reported irregularities.
Updated at 7:35 a.m ET: Andrey Buzin, chief of Golos election monitoring, said it had received more than 1,500 complaints about violations as of Sunday night.
"To me, this election was like a game in which only some players are allowed to compete," Heidi Tagliavini, the head of the European election observers, told reporters at a news conference on Monday.
However, President Dmitry Medvedev described the election as "fair, honest and democratic".
Updated at 5:40 a.m. ET: European monitors said that Russia's parliamentary election has been tilted in favor of the ruling party and marred by violations, The Associated Press reports.
The monitors from the Organization for Security and Cooperation in Europe and other European institutions highlighted issues including limited political competition and a lack of fairness.
Prime Minister Vladimir Putin's United Russia party saw its parliament majority weaken sharply in Sunday's vote despite allegations of widespread violations.
The European observers said the vote was tainted by frequent procedural violations and instances of apparent manipulations, including serious indications of ballot box stuffing.
Earlier, Communist Party leader Gennady Zyuganov dismissed the official results as "theft on an especially grand scale." His party made big gains in Sunday's election.
However, Zyuganov told Reuters that police had barred Communist monitors from several polling stations and "some ended up in hospital with broken bones".
Updated at 4:50 a.m. ET: Prime Minister Vladimir Putin's United Russia received nearly one-third fewer votes than in 2007, Reuters reported.
Communist Party leader Gennady Zyuganovm, whose party was on target to increase its representation from 57 to 92 in the Duma, alleged that some ballot boxes were stuffed before voting began.
"The country has never seen such a dirty election," he added.
Updated at 4:40 a.m. ET: With about 96 percent of precincts counted, Prime Minister Vladimir Putin's United Russia was leading with 49.5 percent of the vote, Central Election Commission chief Vladimir Churov told The Associated Press.
He predicted that it will get 238 of the Duma's 450 seats, a sharp drop compared to the previous vote that landed the party a two-thirds majority in the Duma. The Associated Press described the result as a "humiliating setback" for Putin, "who has steadily tightened his grip on the nation for nearly 12 years."
About 60 percent of Russia's 110 million registered voters cast ballots, down from 64 percent four years ago.
"Sunday's vote badly dented (Putin's) carefully groomed image," The AP's Vladimir Isachenkov wrote. "It reflected a strong public frustration with the lack of political competition, ubiquitous official corruption and the gap between rich and poor, which will pose a growing challenge to Putin's power."
By msnbc.com's F. Brinley Bruton -- published at 3 a.m. ET: Vladimir Putin's ruling party lost its crucial two-thirds majority in parliament in Russian elections held on Sunday, a damaging setback for the country's prime minister who is running for president once again next year.
Meanwhile, Russia’s communists, which seemed to have no future when the Soviet Union disintegrated 20 years ago, drew students, intellectuals, even some businessmen in forging an opposition to Putin's United Russia party, Reuters reported.
The party was running second to United Russia as counting continued on Monday, according to the Moscow Times. While the final results have yet to be determined, initial counting indicates that the party, which the Moscow Times said "crushingly dominated" Russia's politics for years, was set to lose its decisive majority the Duma.
United Russia was set to win about 50 percent of the vote over the weekend, down from 64 percent in the 2007 elections, the newspaper reported.
The results will mean that United Russia will most likely be forced to work with the communists and two other parties that made gains in the elections -- the nationalist Liberal Democratic Party and Just Russia, a social democratic party, The New York Times reported. Over 90 percent of the votes had been counted by Monday morning, the newspaper reported.
"We have received thousands of calls from regional offices, confirming massive violations and fraud," Communist Party deputy head Ivan Melnikov said on the party website, according to the BBC. "Throughout the day, it was like receiving reports from a war zone."
Reuters and The Associated Press contributed to this report.