Prosecutors have launched a fraud case against former prime minister Mikhail Kasyanov. He's accused of faking signatures in support of his formal registration to run for president.

Prosecutors say that more than 15,500 false signatures have been collected in support of Rybinsk in central Russia and the Republic of Mary El in Russia's Volga District.

Kasyanov, who has become an outspoken critic of the Kremlin, has accused it of trying to sabotage his election bid.

In opinion polls, Kasyanov lags far behind leading contender Dmitry Medvedev. The latter is upported by Vladimir Putin and the ruling United Russia party.

Tatyana Chernyshova, an official at the General Prosecutor's Office, outlined the charge against Kasyanov's team.

“From January 8 to January 15, 2008, Kasyanov’s supporters forged 3,500 signatures in the city of Rybinsk, Yaroslavl Region. Since these activities fall under Article 142, part 2, of the Criminal Code, we sent this information to the Rybinsk Department of the Investigative Committee for them to open a criminal case,” Chernyshova said.

“A similar activity has been discovered in the Republic of Mary El. Kasyanov’s supporters there were able to gather only 7,000 signatures, so on January 9 and 10, 2008, they falsified more than 12,000 signatures supporting the candidate,” she added.