Russia's anti-monopoly service said Wednesday it was probing the British energy group BP's crisis-torn local joint venture TNK-BP on request from the state oil giant Rosneft.
The surprise announcement delivers another blow to a lucrative nine-year alliance that provides BP with more than a quarter of its oil output and billions of dollars in annual dividends.
BP last week said it was ready to sell its half in Russia's third-largest oil company after the venture's tycoon CEO Mikhail Fridman resigned and called for either the British or local partners to take full charge.
But it later emerged that TNK-BP's confidentiality rules prevented BP from disclosing important data about the joint venture to suitors that was required for any major divestment deal to go through.
Federal Anti-Monopoly Service deputy head Anatoly Golomolzin said he wanted to require firms to publish their shareholder agreements and was probing whether TNK-BP was keeping Western firms from entering the Russian market.
He revealed that the investigation was initially requested by Rosneft and had been ongoing for "some time".
"We are investigating the (TNK-BP) agreement on behalf of a request by Rosneft," news agencies quoted Golomolzin as saying.
"We received a complaint saying that this agreement may be uncompetitive in nature."
Rosneft's new chief Igor Sechin -- a confidant of President Vladimir Putin who orchestrated a failed tie-up with BP when serving as Russia's energy policy chief -- has denied market rumours about making a bid for the British stake.
The anti-monopoly service announcement however suggests Rosneft is seeking to either acquire or make available to other companies sensitive data about TNK-BP.
The $16 billion Arctic exploration agreement with Rosneft failed primarily because TNK-BP rules required BP to give the joint venture preliminary rights to all its future dealings in Russia.
A favourable ruling by Russia's competition authorities could thus free BP not only to seek a buyer for its half of the company but to also strike new agreements with Rosneft.
Analysts cautioned however that the situation remained fluid and did not seem destined for a quick solution.
VTB Capital said it may be "close to impossible" to find a solution suitable to TNK-BP's bitterly divided Anglo-Russian board.
"Thus, we are reiterating our view that the most likely outcome is the company resuming operations in the former shareholder structure," the Moscow investment bank said.
Rosneft has had difficult relations with the four Soviet-born tycoons who own their half of TNK-BP through the Alfa-Access-Renova conglomerate and are seen by some analysts as an unlikely partner in a new 50:50 venture.
Sechin last week said Rosneft would also be cautious about future dealings with BP because of the Arctic deal's embarrassing last-minute collapse.
BP's place in the offshore exploration venture was taken over by the US supermajor ExxonMobil. Rosneft has since also signed new deals with Norway's Statoil and Italy's ENI but not the British firm.