The dispute over ownership of BP’s joint venture with Russia erupted again yesterday as a senior director abruptly resigned after admitting he could no longer help to resolve the issue.

The departure of Jean-Luc Vermeulen, a former executive of Elf Aquitaine, the French oil group, from TNK-BP came at the end of a week of high drama for TNK-BP and the Russian billionaires who own 50 per cent of the venture. Mr Vermeulen was one of five directors appointed by the Russian side after TNK-BP’s formation in 2003. Five other directors were appointed by BP.

Compounding the company’s problems yesterday, the Tvoi Den newspaper claimed in a front-page story that the Russian Federal Security Service (FSB) had unmasked a senior BP manager as a spy. It did not name the man but published what it said was a photograph of him with his face blurred out.

The paper, which has close ties to the FSB, alleged that the man was linked to Alexander and Ilya Zaslavsky, brothers who were arrested on espionage charges in March. Ilya Zaslavsky had been employed by TNK-BP.

The FSB accused the brothers, who are prominent members of the alumni club of the British Council in Moscow, of collecting classified information on behalf of foreign companies that “wished to have advantages over their Russian rivals”.

The story claimed yesterday that the documents related to the negotiating strategy of Gazprom, the state-controlled gas group, before a Kremlin summit between Vladimir Putin, the Russian Prime Minister, and President Yushchenko of Ukraine. It said that details of Gazprom’s development plans to 2020 had also been leaked.

The link with Gazprom appeared to be the latest element in an intense Kremlin campaign to force TNK-BP, Russia’s third-largest oil producer, to turn over its assets to a state-controlled company. Last year it was forced to sell to Gazprom a controlling stake in the giant Kovykta gasfield in Siberia.

Gazprom, whose former chairman is President Medvedev, is seen as the most likely beneficiary of a sale. Neither BP nor the three Russian billionaires who own 50 per cent of the company have expressed willingness to sell.

However, bitter divisions emerged this week between BP and its Russian partners – Viktor Vekselberg, Mikhail Fridman and Len Blavatnik. The Russians boycotted a board meeting on Thursday after BP rejected their demand for the resignation of Robert Dudley, the chief executive of TNK-BP. They accused Mr Dudley, who has managed the company since its creation, of serving only BP’s interests.

A spokeswoman for TNK-BP dismissed the spying allegations as “absolutely groundless”.

A spokesman for BP in London expressed strong support for Mr Dudley. He said that BP had “absolute confidence” in Mr Dudley’s ability to represent the interests of all shareholders.

The Kremlin’s campaign against foreign ownership of Russian energy resources forced Shell to cede control of the $20 billion (£10 billion) Sakhalin-2 oil and gas project to Gazprom last year. As the only big energy company not under Russian control, TNK-BP is firmly in its sights.

The Interior Ministry said on Thursday that an executive employed by TNK before its link-up with BP was being accused of evading nearly $1 billion in taxes.

The FSB raided the Moscow offices of BP for the second time last week, in the wake of searches conducted at both TNK-BP and BP when the Zaslavskys were arrested.

Soon after those raids BP was forced to suspend 148 technical specialists seconded to TNK-BP in a dispute over visas.

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