MOSCOW, February 5 (RIA Novosti) - Russia's Supreme Court upheld on Tuesday a decision by election authorities to bar opposition candidate Mikhail Kasyanov from running in the March 2 presidential election.

Former prime minister Kasyanov was denied registration as a presidential contender after the Central Election Commission (CEC) ruled that over 13% of signatures collected to support his bid were either fake or unverifiable. His support team rejected the forgery claims as "political pressure."

The ex-premier's lawyer, Vadim Prokhorov, said on Tuesday he would appeal the Supreme Court's decision.

Under Russian law, candidates not nominated by parliamentary parties have to collect at least 2 million signatures in their support. The share of invalidated signatures cannot exceed 5% of the total.

Four candidates have passed registration procedures: First Deputy Prime Minister Dmitry Medvedev, Communist leader Gennady Zyuganov, the ultranationalist Liberal Democratic Party leader Vladimir Zhirinovsky and Andrei Bogdanov, the leader of the tiny pro-Western Democratic Party.

Medvedev, who has been publicly backed by President Putin, is the clear front-runner.