The only liberal Kremlin critic in Russia's presidential race stands to be kept off the ballot because tens of thousands of signatures on his nominating petitions were forgeries, election officials said Thursday.

The Central Election Commission is expected to make a formal ruling later in the day.

Opinion polls gave former Prime Minister Mikhail Kasyanov little chance of posing a significant challenge to President Vladimir Putin's hand-picked successor, Dmitry Medvedev, in the March 2 vote. Kasyanov, however, could have been an embarrassment for Putin and Medvedev because of his harsh criticism.

The denial of registration to Kasyanov would likely fuel criticism of the election as undemocratic and stage-managed by the Kremlin.

Presidential aspirants not affiliated with political parties must submit 2 million signatures supporting their bid to get on the ballot. Kasyanov's campaign said it turned in 2,067,000 signatures.

But Nikolai Konkin, secretary of the Central Elections Commission, said a check of the signatures found more than 80,000 to be invalid.

"That means the number of reliable signatures is less than 2 million, which is the basis for the denial of registration," Konkin said in a statement.

Registration can also be denied if more than 5 percent of an aspirant's signatures are found to be invalid; Konkin said more than 13 percent of Kasyanov's signatures were bogus in two large samples of the total submitted.

On Tuesday, the prosecutor-general's office also opened a forgery case against the campaign of Kasyanov, who was Putin's first prime minister but became a critic after his dismissal in 2004.

Kasyanov, speaking on a trip to Brussels, told AP Television News the election officials' statement about forged signatures was "simple propaganda."

Kasyanov said that if he were kept off the ballot, Putin would be to blame. "It's not up to the Central Election Commission, it's up to Vladimir Putin," he said Tuesday.

Medvedev faces no strong challengers, and other liberal Putin foes who sought to mount campaigns, including chess great Garry Kasparov, have accused the Kremlin of forcing them out of the race.

Medvedev's approval ratings soared after Putin named him as his preferred successor last month, boosted by positive coverage by national television stations, all controlled by the Kremlin. The latest opinion poll, released this week by the All-Russia Opinion Research Center, which also has links to the Kremlin, had more than 60 percent of respondents saying they would vote for Medvedev.

The nationwide poll of 1,600 people had a margin of error of 3.4 percentage points.