Shares in beleaguered Russian oil firm Yukos tumbled another 10 per cent yesterday on reports that the government would sell its main production unit for a quarter of its real value to pay off the company's multibillion-dollar tax arrears.

The latest crash in the value of what was one of Russia's blue-chip stocks was prompted by reports from a well-connected local news agency that a controlling stake in Yukos's Yuganskneftegaz subsidiary would be sold for just $4 billion (€3.2 billion).

An unnamed government source was also quoted as saying that a company affiliated with the state-controlled gas giant Gazprom would probably be a bidder. This, in conjunction with the reported $4 billion price tag, "implies confiscatory nationalisation", Moscow's UFG brokerage wrote in a note to its clients.

The year-long legal onslaught against Yukos is seen by many as an attack on the company's founder, Mr Mikhail Khodorkovsky, who was President Vladimir Putin's most powerful domestic critic but who now faces jail for alleged fraud and tax evasion.

Analysts were stunned this week when the Justice Ministry said Yuganskneftegaz would be sold for $10.4 billion, taking the figure from a report by Dresdner Kleinwort Wasserstein.

The bank insisted afterwards that the government had taken the report's "worst-possible-scenario" figure as a reasonable value for the operation, instead of other estimates closer to $17 billion. Yukos values the unit at about $30 billion.