A statement from the Central Election Commission Monday morning said United Russia, chaired by Prime Minister Vladimir Putin, won 238 seats in the 450 seat house – or 49.54 percent of the vote.
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That's down from 315 seats – or 64 percent – in the last elections, in 2007.
United Russia’s biggest opposition will be the revived Communist Party, which in a surprise boost, increased its number of seats to 92 from a previous 57, Radio France Internationale reported.
Russia’s Kommersant newspaper reported Monday that the results mean a change in the way United Russia governs, saying the party will need to “look for partners."
United Russia's poor showing comes after Putin announced he would again run for president next March.
The vote is effectively being seen as a popularity test for Putin, the BBC reported.
The network said opposition parties and an independent monitoring group had complained that electoral rules were broken in the lead up to the vote.
The independent monitoring group Golos said it had logged 5,300 complaints.