Election officials said Tuesday that Yabloko candidate Grigory Yavlinsky would be disqualified from running for president in March, a move that would prevent his party from fielding observers.

Central Elections Commission secretary Nikolai Konkin said the body would formally block Yavlinsky from the ballot later this week, after finding that hundreds of thousands of the signatures submitted on his nominating petition were invalid.

The elections commission already has registered Prime Minister Putin and three other contenders: Communist Party chief Gennady Zyuganov, Liberal Democratic Party leader Vladimir Zhirinovsky and Just Russia leader Sergei Mironov. Since their parties are represented in the State Duma, their registration is easier than for other potential candidates.

The rejection of Yavlinsky's candidacy, however, is likely to sharpen political tensions that have been strong since last month's unprecedented massive protests sparked by alleged fraud in the Duma elections.

Although Yavlinsky has not been a key figure of those protests, his party fielded thousands of election observers in the December elections who documented evidence of fraud in favor of Putin's United Russia party.

On Monday, Yavlinsky said authorities wanted to prevent him from running in order to block genuine competition. He says other candidates are only nominal rivals and are following Kremlin guidance.

Yabloko has not had any seats in the parliament since 2007. Politicians who want to run for president but whose parties are not in the Duma must submit 2 million signatures in support of their candidacy.

Konkin said examinations of about 600,000 of the signatures submitted to support Yavlinsky's nomination found that some 25 percent were invalid, largely because the signatures were photocopied. That is higher than the 5 percent rejection level allowed by law.

"At the end of the week, the Central Elections Commission will hold a session at which the registration of Yavlinsky will be officially refused," he said, according to RIA-Novosti.

By excluding him from the presidential race, the commission would prevent Yabloko from sending observers for the presidential election. Observers at the polls can only be named by participants in the race.