Russian President Vladimir Putin's party has won a landslide election victory, official results show.

With more than 80% of ballots counted, his United Russia had 63% of the vote. The opposition Communists and two other parties were also poised to win seats.

Opposition allegations of fraud were dismissed by the electoral commission.

Putin has said a strong result would give him the authority to retain political power after his presidential term ends next year, possibly as PM.

The Communists say they will mount a legal challenge to the result. They said a meeting would be held later on Monday to decide whether to boycott the new parliament.

"We do not trust these figures announced by the central elections commission and we will conduct a parallel count," Communist Party leader Gennady Zyuganov said.

The White House also urged Russian authorities to investigate reports of fraud.

United Russia's leader, Boris Gryzlov, acknowledged there had been violations but dismissed them as insignificant.

"They in no way put in doubt the final result. The fact that these violations have been registered shows that we have a transparent ballot," he said.

Independent monitors have complained their attempts to observe the poll were hampered.

The Organization for Security and Co-operation in Europe (OSCE) abandoned its plans to send a big team of election observers, accusing Moscow of imposing curbs and delaying visas. Russia denied the claims.

Only a much smaller group of MPs from the OSCE's parliamentary assembly attended the election, leaving some 330 foreign monitors covering 95,000 polling stations.

The independent Russian monitoring group Golos reported various violations it said amounted to "an organised campaign", including:

 Entering those voting for United Russia into a prize lottery, reported in St Petersburg

 Transporting voters by bus between polling stations, to vote multiple times, in Moscow and St Petersburg

 Opposition party observers being detained for "looking suspicious", in Samara

 Voters being given ballots already filled out for United Russia, in Pestovo

However, the chairman of the Central Election Commission, Vladimir Churov, told Russian television he knew of "no serious violations in the course of polling day".

Eleven parties were competing for places in the lower house, the Duma.

But apart from United Russia, only three polled the minimum of 7% to enter parliament, according to partial results - the Communists, A Fair Russia and the right-wing Liberal Democratic Party.

The latter two are allied to United Russia, meaning parties loyal to the Kremlin are expected to have 348 seats in the 450-seat parliament, according to a state-owned polling agency.

This would give United Russia and its allies enough support to push through possible changes to the constitution.

Gryzlov of United Russia said the election was "a referendum on President Putin so I think we can say he has won a victory".

The party will nominate its candidate for next year's presidential elections at a congress later this month, Gryzlov said.

Options for Putin

Putin is constitutionally obliged to stand down after his second term as president ends in March next year.

According to the BBC's James Rodgers in Moscow, his party's apparent landslide win in Sunday's election will enable him to continue wielding great influence in politics - even if he is no longer in high office.

Putin announced earlier this year that he may seek the office of prime minister after his presidential term ends.

If predictions are right and the Liberal Democratic Party enters parliament, it means its candidate Andrei Lugovoi would be guaranteed a seat.

Lugovoi is wanted in Britain over the murder of former Russian spy Alexander Litvinenko, but a parliamentary seat would grant him immunity from prosecution and extradition.

PHOTO CAPTION 

United Russia party chief Boris Gryzlov speaks at the party's headquarters in Moscow. [Reuters]

BBC