Vladimir Putin at a polling station in Moscow, 02 Dec 2007

At least two Russian opposition parties say they plan to challenge the results of Sunday's parliamentary elections, which President Vladimir Putin's party has won in a landslide.

With more than 90 percent of the votes counted, the United Russia party has more than 63 percent of the ballots cast, followed by the Communist Party, with almost 12 percent.

Two pro-Kremlin parties (the Liberal Democratic party and Fair Russia) also won enough votes to qualify for seats in the Duma (- the lower house of Russia's parliament).

Leaders of the Communists and the Union of Right Forces party both plan to challenge the results.

Kimmo Kiljunen, a senior European lawmaker who observed the election, says the vote was problematic because of the executive branch's strong influence on party politics.

Under Russia's new election laws, voters no longer choose individual candidates, but instead vote for parties, which decide who sits in parliament.

The constitution bars Mr. Putin from running for a third straight term in Russia's presidential election next March, but a United Russia-dominated parliament could back him as prime minister and allow him to head the next government.

Opposition members have complained for several weeks that the Kremlin was rigging the election in favor of the pro-Putin party. They contend that opposition voices were denied access to Russian media, and that riot police broke up rallies and arrested their leaders.

Election monitors from the independent group Golos reported Sunday that the campaign was marked by "unprecedented pressure" on voters.

Some Russian voters said they had been threatened with the loss of their jobs if they did not support United Russia. Others said their ballots were already filled out when they arrived at polling places Sunday.

Russian election chief Vladimir Churov said voting went smoothly, but the White House is urging Russia to investigate all claims of voting fraud.

Some information for this report was provided by AP and Reuters.