Prosecutors opened a new criminal probe on Thursday into the Media-MOST company, the latest challenge to the media group at the center of a swirling political and business controversy.

Prosecutors said in a statement that they are investigating whether Media-MOST, the nation's biggest private media company, had illegally transferred assets abroad to hide them from Russia's natural gas monopoly, which is trying to take over Media-MOST.

Fraud charges filed in a separate case against Media-MOST chief Vladimir Gusinsky in June were dropped the following month.

The latest probe followed an appeal least week from natural gas giant Gazprom, which is the largest creditor of Gusinsky's group.

Media-MOST rejected that charge in a statement. "The restructuring of a number of the holding's companies was conducted absolutely legally," read the statement carried on Interfax. "Gazprom did not offer any objections on this score before turning to the prosecutor's office."

Prosecutors' dogged pursuit of Media-MOST has led some press freedom advocates to speculate that President Vladimir Putin is trying to silence Gusinsky's news outlets, including the flagship NTV television station, which have been critical of the Kremlin.

Gusinsky is one of Russia's so-called oligarchs, men who used their Kremlin connections to amass huge personal fortunes in suspicious privatization deals. Since his ties with the Kremlin withered, NTV and other outlets have run scores of stories on official corruption and allegations of government incompetence.

Gusinsky was jailed for four days in June on charges of defrauding the state in a privatization deal. He denied the charges and said that prosecutors were acting on the Kremlin's political orders.

He then signed a tentative agreement in July to sell Media-MOST to Gazprom. But Gusinsky recently declared the agreement void, saying he had signed the deal under duress in exchange for his freedom and the dropping of the fraud charges.

Gusinsky accused the Kremlin of pushing Gazprom to gain control of Media-MOST, saying its involvement was proven by the appearance of Press Minister Mikhail Lesin's signature on the document. Lesin insisted he signed the agreement as a personal favor to Gusinsky, and he has since acknowledged that it was a mistake.

Putin has reiterated that the government wasn't part of the conflict and has suggested that Media-MOST and Gazprom solve their dispute in court.

Prime Minister Mikhail Kasyanov gave Lesin a televised dressing-down at a Cabinet session Thursday, following a similar scolding during a one-on-one meeting last weekend.

"You haven't been minister for a month yet, and you must remember that public service, and especially the post of federal minister, imposes a number of limits that must be observed," Kasyanov told Lesin.

Gazprom claims its efforts to acquire Media-MOST stock are not politically motivated. Media-MOST owes the gas giant hundreds of millions of dollars.

Gusinsky, who is currently abroad, has been summoned to appear for more questioning by prosecutors, but his lawyer Genri Reznik said he would advise his client against showing up because "there are no security guarantees."