Lebedev is already in custody

Platon Lebedev, one of Russia's richest men, is already facing three charges, including theft of state property during a 1994 privatisation deal, and is currently in custody.

Russian business has been rocked by a judicial investigation into the privatisation and by a probe into Yukos' tax position.

The investigation has raised fears that the Kremlin will re-examine the results of the 1990s sell-off of state property that made a handful of tycoons - the so-called oligarchs, including Mr Lebedev - into billionaires overnight.

Putin and Kasyanov criticised detention of businessmen

The Russian authorities are investigating both Yukos and rival firm Sibneft, which are due to merge to create the world's fourth-ranked producer.

Yukos chief executive Mikhail Khodorkovsky, who is a close ally of Mr Lebedev and has a personal fortune estimated at $8bn, has been targeted by prosecutors in what is seen as a politically-driven campaign by Kremlin figures.

However, both President Vladimir Putin and Prime Minister Mikhail Kasyanov have described the detention of businessmen suspected of economic crimes as excessive.

Interfax news agency quoted Natalya Vishnyakova, another spokeswoman for the Prosecutor-General's Office, as saying that such statements could be construed as pressure on the courts.

"There is an opinion among the people that if you steal a little you'll go to prison but if you steal a lot you'll escape responsibility," she said.

"We're trying to reject that point of view."