While Prime Minister Vladimir Putin's United Russia party claims sweeping victory in regional elections, opposition leaders say the vote was rigged. 

According to official results reported Monday, United Russia captured a wide margin in elections which are being widely viewed as a test of Russia's democracy.

Leonid Ivlev, a member of the Central Elections Commission, told reporters that the ruling party had garnered almost 80 percent of seats up for grabs in the 75 regional and local elections held up and down the country on Sunday.

Ivlev said Putin's party picked up 107 of the 135 regional seats and 189 of the 235 seats available in municipal legislatures.

They also emerged victorious in the eagerly-watched race for Moscow's city legislature. With 99 percent of votes in, the RIA-Novosti news agency reported a 66 percent win for United Russia.

Russian President Dmitry Medvedev has promised to encourage multiparty democracy since his election last year. Sunday's regional elections will put this pledge to the test, with opposition claiming little improvement. 

Elections for regional, district and mayoral offices are being held on Sunday in 76 of the country's 83 administrative regions, with 30 million voters expected to visit the polls. One of the most criticized races is that for Moscow's city council and mayor, who control a municipal budget of $40 billion (27 billion Euros). Of the six parties registered, all but one are pro-Kremlin.

Pro-Western parties said that all of their candidates were barred from running for 17 directly elected seats on the council after city officials declared the signatures on their registrations invalid.

The leader of the sole party allowed to enter the race for 18 party seats said they had been blocked from advertising on television or in newspapers and even in posters on the street.

The pro-Kremlin party dominated an election for Moscow city council and other local votes across Russia, results released Monday showed.

With 99 percent of the Moscow vote counted, United Russia won 66 percent and the Communist Party 13 percent. No other party cleared the 7 percent threshold to win seats on the city council.

United Russia is a power base for Vladimir Putin, now the prime minister and party head, who has not ruled out a return to the presidency in 2012. President Dmitry Medvedev congratulated party leaders on their "convincing" victory, which he said showed "the authority the party has acquired from our people in recent years."