Russians have begun voting in key parliamentary elections, in which the ruling party of Prime Minister Vladimir Putin is widely expected to claim victory.

Russians have begun voting in key parliamentary elections, in which the ruling party of Prime Minister Vladimir Putin is widely expected to claim victory.

Polls opened on Sunday across Russia, with 3,000 candidates from seven political parties competing for the 450 seats in the lower house of parliament, Duma.

Around 55 percent of the 110 million eligible voters are expected to cast their ballots.

The elections are seen as a major test for Putin and his United Russia party to stay in power as he prepares for the March presidential vote.

Polls show the ruling United Russia party has high chances to win Duma's majority; however, it will obtain less than the 315 seats it currently holds.

Putin's party needs to win more than two-thirds of the seats, otherwise it will not obtain constitutional majority which allows it to amend the constitution and even approve the impeachment of the president.

Meanwhile, opposition parties have called the elections unfair, saying the authorities financially support Putin's party.

Putin, 59, formally accepted to stand as the ruling party candidate in the 2012 presidential elections to be held in March.

Putin's presidency ended in 2008 after two consecutive terms because the Russian constitution prevented him from running a third term.

However, he will be free to run again in 2012 as President Dmitry Medvedev changed the constitution in late 2008 to extend future presidential terms to six years.