Russia today disqualified the sole liberal challenger to Vladimir Putin in March 4 presidential elections, in a move slammed by his supporters as undermining the legitimacy of the polls.

Russia's central elections commission said it could not accept nearly a quarter of the registration signatures gathered by Grigory Yavlinsky because they were either photocopies of originals or fakes.

"I am sad to announce that we will not able to register Yavlinsky as a candidate," election commission member Sergei Danilenko told a special hearing.

Russia's strict presidential election rules require all independent candidates whose parties fail to win seats in parliament to collect two million signatures to win registration.

The restriction has been heavily criticised by the candidates as well as the growing protest movement against Putin, who will be standing for a third Kremlin term in the polls after his four year stint as prime minister.

The disqualification "undermines the legitimacy of the vote. This was ordered directly by Putin," said Sergei Mitrokhin, chairman of the liberal Yabloko (Apple) party that Yavlinsky founded in 1993.

Mitrokhin added that the authorities were particularly keen to make sure that Yabloko -- which sent thousands of observers to December's parliamentary elections -- was barred from monitoring the presidential vote.

"One of their main goals was to keep our observers out," Mitrokhin told AFP.

Putin's spokesman called Mitrokhin's comments unfair.

"If one of the candidates fails to collect the required number of signatures, this does not mean you can make claims about the vote's illegitimacy," Dmitry Peskov told the RIA Novosti state news agency.

Putin had doubled the number of signatures required for candidates' registration in 2004, a year in which he stepped up his campaign to centralise power by also announcing an end to direct elections for regional governors.

The presidential election rules were tightened again in 2007 when Putin was about to hand power over to his hand-picked successor Dmitry Medvedev, giving candidates just a month to rally their support instead of the previous three.