The Russian special prosecutor, Nikolai Volkov, who has been investigating high-level government corruption, has resigned, reportedly under pressure from his bosses for inviting Swiss prosecutors to visit Russia.

The Russian prosecutor general's office said the 48-year-old had asked to take early retirement after 20 years in law enforcement. But in interviews with the Russian media, Volkov hinted that his position had become untenable.

"Either I am able to work or not. I will not be in anyone's pocket," he said.

Volkov said the immediate cause of his departure was that he had asked Swiss prosecutors for evidence without first clearing that request with the acting prosecutor general, Yuri Biryukov.

"They consider I made a mistake that cannot be excused. I admit it, I understand and I raise my hands in surrender."

Volkov had been probing allegations that the Russian media magnate, Boris Berezovski, was involved in embezzling money from the state airline, Aeroflot, through two Swiss companies, Forus and Andava. His investigations brought him to Switzerland several times, most recently at the end of July.

At the end of his last visit to the Swiss capital, Berne, Volkov said the hundreds of documents the Swiss authorities had given him could provide crucial evidence that would enable him to bring charges against Berezovski. He said he would decide by September whether or not to press charges.

Volkov confirmed that more than $900 million had been passed through Swiss firms.

Some Russian media reports speculated that Volkov had been too open with the Swiss media during his visits to gather information.

As well as the Aeroflot investigation, Volkov also led a probe into allegations that top officials in President Yeltsin's government took bribes from a Swiss construction company, Mabetex.

It's not clear who will take over the investigations, now that Volkov has stepped down.

swissinfo with agencies

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