Gazprom showed its hand today in the battle over the future of TNK-BP after confirming an interest in buying into the Anglo-Russian oil giant.

As TNK-BP's chief executive, Robert Dudley, was being grilled by Russian police, Gazprom declared that it was keen to take a stake in its rival.

However, Alexander Medvedev, its deputy chief executive, said that Gazprom would wait until TNK-BP had resolved the conflict between its British and Russian investors.

"Our shareholders said a year ago that if shares were put up for sale, Gazprom would consider a possible purchase," Mr Medvedev said: "For the moment there is a conflict among the shareholders in the company."

Mr Medvedev said that Gazprom would review its position "after the conflict is settled" at TNK-BP. Many analysts believe, however, that the Kremlin is behind the dispute as part of a campaign to push Russia's third largest oil producer into the clutches of a state-owned company such as Gazprom.

TNK-BP is 50 per cent owned by BP and 50 per cent by Russian billionaires, Viktor Vekselberg, Mikhail Fridman, German Khan and Len Blavatnik. The Russian partners have demanded Mr Dudley's resignation, accusing him of acting only in BP's interests.

Mr Dudley spent almost five hours at an Interior Ministry office in Moscow today as police quizzed him as part of a tax investigation. He described the meeting as "very routine", adding: "There were no problems. It was a review of TNK. We did not discuss counterparts....routine matters, by the law, very professional."

A company spokeswoman said that he had been questioned as a witness over tax payments at TNK between 2001 and 2003.

TNK is a former subsidiary that no longer exists after the joint venture with BP was formed in 2003. TNK-BP retains legal responsibility, however, although Mr Dudley has never worked for TNK.

His interview at the Interior Ministry came a day after prosecutors demanded masses of documents from TNK-BP as part of a separate inquiry into alleged violations of immigration and employment law. Company officials handed over documents to investigators, who demanded more.

TNK-BP has been the target of relentless official pressure in recent months. The Federal Security Service, (FSB), searched TNK-BP's headquarters after charging an employee with industrial espionage in March, and agents have twice raided BP's Moscow offices.

BP's chief executive Tony Hayward flew to Moscow last week to try to defuse the crisis. He warned the Kremlin that Russia was putting its international reputation at risk, arguing that property rights and the rule of law were "key to the continued successful transformation" of its economy.

TNK-BP accounts for a quarter of BP's worldwide output and made a net profit of $5.3 billion last year. The dispute between BP and the Russian shareholders centres on differences over international expansion plans.

Gazprom has been seen as favourite to take control of the company. But an unidentified government official poured cold water on the idea at a prestigious international economic forum in St Petersburg at the weekend.

Another potential bidder is state-owned Rosneft, whose chairman is Igor Sechin, the shadowy vice prime minister responsible for energy policy. BP is also a minority shareholder in Rosneft, Russia's largest oil company.

The struggle over TNK-BP is taking place at a time of soaring energy prices. Gazprom's chief executive Alexei Miller predicted that the price of oil would almost double next year to $250 per barrel from $134 now.

Gazprom, which supplies a quarter of Europe's gas needs, is the world's largest gas producer. Mr Miller said that its stock market valuation would triple to $1 trillion within the next decade, making Gazprom the world's most valuable company.

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