Former Russian prime minister Mikhail Kasyanov, who has suggested he might run for president in 2008, said Monday that a criminal probe of his acquisition of a state-owned villa in Moscow was part of an attempt to remove from the political arena any candidate not sanctioned by the authorities.

Kasyanov, 47, issued a statement hours after returning to Moscow from vacation, ending rumors that he might remain in exile rather than face possible charges over a series of real estate deals in which he allegedly acquired the villa for the cut-rate price of $370,000.

Alexander Khinshtein, a member of parliament from the Kremlin-backed United Russia party, has charged that the villa was worth at least $29 million and was hastily auctioned off by the state while Kasyanov was prime minister. That accusation ostensibly prompted the investigation by the general prosecutor's office.

The newspaper Izvestia reported that the villa and a lease on the property were acquired separately by companies that were registered on the same day at the same address, suggesting they were fronts.

Amelia, the company that bought the villa, acquired it in January 2004, when Kasyanov was still prime minister. Amelia sold the property to Kasyanov in August 2004, after he had been fired as prime minister by President Vladimir Putin, according to the newspaper's reading of the real estate documentation.

State prosecutors are investigating whether Kasyanov orchestrated a bogus auction with a view to acquiring the property in his own name later.

"I have returned to Moscow in spite of all the threats being made against me," Kasyanov said in the statement. "I have absolutely no doubt that this libelous campaign to discredit me, which is based on a lie and distorted facts, comes as part of the authorities' general strategy aimed at 'clearing' the political field."

He has not given a response to the details of the claims against him.

In recent months, Kasyanov has become increasingly critical of Putin, and some analysts here have suggested that the investigation was a warning from the Kremlin that he should back off or face having his past scrutinized. Claims of corruption have shadowed Kasyanov since his days in government.

Kasyanov restated his criticism of the government in Monday's statement. "The authorities are losing touch with their people," he said. "Creating an environment for a real political process, which envisions public discussions on a variety of opinions on the situation in the country and an opportunity to choose among them freely, is the task I will continue to tackle."