Russian state oil firm Rosneft moved last week to take control of stricken oil major Yukos's key unit, Yuganskneftegaz, bought at a controversial auction which Yukos is challenging in the US courts.

A Yukos official said a Rosneft delegation, which arrived last week at Yugansk's Siberian hometown of Nefteyugansk, was claiming Rosneft had already fully paid $9.4 billion for the purchase of Yugansk to the state.

Rosneft, MDM and the Russian Federal Property Fund, which auctioned Yugansk on December 19, were all unavailable for comment.

"They arrived today and the delegation is headed by Rosneft's first vice-president Nikolai Borisenko," a Yukos official said.

"The have arrived with bailiffs and are currently presenting to our Yugansk employees their new boss, Vladimir Bulba, head of (Rosneft unit) Purneftegaz.

"Rosneft claims they have fully paid for Yugansk via MDM bank, have shown us some documents and want to hold an extraordinary general meeting today after changing the registrar," the official said.

The Yugansk auction marked the climax of a Kremlin campaign to crush Yukos's politically ambitious principal owner, Mikhail Khodorkovsky, and seize control of strategic sectors of the economy sold off in the chaotic privatisations of the 1990s.

Yugansk, which pumped one million barrels per day of crude, or 60 per cent of Yukos's output, was sold to help recover back taxes owed by Yukos of over $27 billion.