Russian billionaire Mikhail Prokhorov was officially registered as a presidential candidate Wednesday, the only political newcomer allowed to challenge Prime Minister Vladimir Putin for the Kremlin job.

The three others on the ballot for the March vote are veteran party leaders who pose little challenge to Putin, who is seen as all but certain to win the election and return to the post he held from 2000 to 2008.

Putin, however, is under heavy pressure to show that he can win a fair election. Evidence that vote rigging boosted the results of his party in the Dec. 4 parliamentary election led to mass protests in Moscow. Another demonstration to demand free elections is planned for Feb. 4.

Prokhorov, who owns the New Jersey Nets basketball team, is a 46-year-old businessman with an estimated fortune of $18 billion. His candidacy has been viewed as a Kremlin-supported effort to add a veneer of legitimacy to the election and channel the discontent among Russia's urban middle class, the core of the anti-Putin protest movement.

Prokhorov insists he is acting independently of the Kremlin, but he has refrained from criticizing Putin directly and has said he would consider serving as Putin's prime minister.

On Wednesday, Prokhorov once again denied that his candidacy was a "Kremlin project."

"I've always been my parents' project. And I've always made decisions on my own," Prokhorov said. "To disprove any opinion or any rumors, there is such a thing as life. You should look at who's proposing what and who's made what with their own hands. That's the best proof of what you are."

The Central Election Commission's decision Wednesday to register Prokhorov came a day after it blocked the candidacy of prominent opposition leader Grigory Yavlinsky.

Politicians who want to run for president but whose parties are not in parliament must submit 2 million signatures in support of their candidacy. The commission ruled that too many of the signatures submitted in support of Yavlinsky were invalid, while those for Prokhorov met the requirements.

Yavlinsky's liberal party, Yabloko, had fielded thousands of observers in the December election and they were among the most aggressive in documenting evidence of fraud in favor of Putin's United Russia party. Yavlinsky's exclusion from the presidential race denied his party the right to have observers at the March 4 vote.

The green light given to Prokhorov was seen as further evidence that his candidacy has Kremlin approval. His message of evolutionary rather than revolutionary change seems designed to appeal to those who see no alternative to Putin but would like to see democratic reforms.

A poll conducted last month by the independent Levada Center showed voter support for both Yavlinsky and Prokhorov in the low single digits.

Putin's strongest rival is Communist Party leader Gennady Zyuganov, a veteran of three previous presidential elections whose party has reached an accommodation with Putin over the years. The other two candidates are only nominal rivals.