Peter Mandelson, the European Trade Commissioner, accused Russian shareholders in TNK-BP of menacing behaviour yesterday in the struggle for control of the oil joint venture.

Mr Mandelson, attending the EU-Russia summit here in Siberia, said that the dispute over the embattled oil giant was damaging Moscow's image with international investors. He described the conflict between BP and the quartet of Russian billionaires who own half of the company as “primarily an issue between shareholders”. But he added that it raised wider questions about Russia's relationship with the European Union and with international investors.

“The first is the somewhat menacing behaviour on the Russian shareholders' part towards corporate governance and the management of TNK-BP, which is a Russian company,” Mr Mandelson said. “The second is the use of state resources, apparently, to back up the position of the Russian shareholders. This raises questions about the climate for international investment in Russia, about the operation of the rule of law and about the relationship of the state, its agencies and resources, to what should be purely a private-sector business relationship.”

TNK-BP, which was formed in 2003, has come under sustained attack from government bodies in Moscow since the corporate war erupted between BP and its Russian partners Mikhail Fridman, Viktor Vekselberg, Len Blavatnik and German Khan.

It is the target of a tax investigation and a separate inquiry into alleged violations of immigration and employment law. Robert Dudley, TNK-BP's chief executive, was summoned for a five-hour interrogation by Interior Ministry police this month as part of the tax inquiry. TNK-BP's headquarters were raided by the FSB, the federal security service, after an employee was charged with industrial espionage.

The Russian shareholders' AAR consortium has demanded the dismissal of Mr Dudley, accusing him of running the company solely in the interests of BP. But BP said this week that it was absolutely committed to Mr Dudley.

Suspicions persist that Russia's third-largest oil company is the target of a Kremlin-backed campaign to force it to cede control to a state-owned rival such as Gazprom.

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