According to preliminary results, United Russia has won a landslide victory in 13 of the regions, trailing only the new Just Russia party in the Stavropol Territory. The Communists (KPRF) and the ultra-nationalist Liberal Democratic Party of Russia (LDPR), which are also represented in the State Duma, took third and fourth place, respectively, in most regions.
The regional ballots held in 14 regions across Russia, involving about a third of the country's electorate, are regarded as a dress rehearsal for elections to the State Duma, the lower house of the Russian parliament, scheduled for December 2.
Vyacheslav Nikonov, head of the Moscow-based think tank Politika, told RIA Novosti that "four parties are likely to pass the 7% threshold - United Russia, KPRF, LDPR and Just Russia."
He said the Union of Right Forces (SPS) may also be successful while others have little chance.
Sergei Markov, the director of Moscow's Political Research Institute, hailed the "tremendous" success of the United Russia, which can expect a majority in the new State Duma, and the debut of Just Russia, which will compete with the Communists for second place.
"I believe that the structure of the State Duma has been clearly established," he said.
"SPS also has some chances. These elections demonstrate that it is not all over as many thought," he said.
State Duma Speaker and United Russia leader Boris Gryzlov said SPS will gain seats in the lower chamber during the December elections.
He said the party will win 7-9% of the vote.
"We have to build the economy with consideration of right-wing opinion," Gryzlov said.
He said United Russia won 45% of the vote, KPRF - 16%, Just Russia - 15% and LDPR - 11% in the March 11 elections, according to preliminary results.