Russian billionaire Mikhail Prokhorov, who hopes to challenge Prime Minister Vladimir Putin in a presidential election next March, is exploring a bid for the influential daily Kommersant to back up his campaign.

A source at Onexim, Prokhorov's investment fund, told Reuters that Onexim was in the early stages of negotiations to buy the Kommersant publishing house from tycoon Alisher Usmanov.

The source, who spoke on condition of anonymity but is directly involved in the negotiations, said the deal had a political component and Usmanov was expected to respond on Wednesday:

It would be strange if I said a deal for a paper such as Kommersant was a purely commercial one. It's clear that it's not only commercial, that it is a political instrument.

Prokhorov announced Monday that he would run for president against Putin, who remains Russia's most popular politician even though his ruling United Russia party saw its vote slide sharply in this month's parliamentary election.

The tycoon, who needs 2 million signatures or a party nomination in order to run, has presented himself as a champion of a growing middle class who feel United Russia, still easily the dominant party, does not adequately represent their interests.

Many of the tens of thousands of people who have taken to the streets to protest against alleged ballot rigging since the election have been from the middle classes. More protests are expected later this month.

The daily Kommersant, which has reported extensively on the public discontent since the election, is the main publication in the stable of the same name, with a circulation of over 100,000 mostly middle-class readers.

EDITOR FIRED

Prokhorov's decision to run was cheered by some of the protesters although others said that the announcement was part of the plot by the Kremlin to appease liberal-minded Russians who have grown tired of Putin's dominance in politics.

Usmanov, whose business interests range from metals to the internet, provoked outrage among opposition supporters when he fired an editor for publishing a photograph featuring an obscene message addressed to Putin.

The move was widely seen as a reflection of official anger at Kommersant's coverage of the protests, and evidence of the vast influence the state holds over Russian media.

Usmanov confirmed to Kommersant FM radio that Prokhorov had contacted him about a purchase, but said that he had responded by saying that he appreciated the joke.

Access to media outlets is likely to be essential for Prokhorov if he wants to mount a serious challenge against Putin, who enjoys favourable coverage from national television channels and other Kremlin-friendly media.

Prokhorov, a 46-year-old metals tycoon who owns the U.S. New Jersey Nets basketball team, has a fortune estimated by Forbes magazine at $18 billion (11 billion pounds). He holds a stake in the aluminium giant RUSAL and is chairman of Polyus Gold, Russia's largest gold producer.

He is also sitting on a pile of cash after selling off some of his assets before the economic crisis hit Russia in autumn 2008.

The source confirmed that Prokhorov was also looking at other media assets, including TV Dozhd (Rain TV) a niche television channel aimed at educated urban Russians.

(Reporting by Gleb Bryanski; Editing by Kevin Liffey)