Russian oil group Yukos has been sold off at auction.

The final auction to dispense with assets belonging to the bankrupt company has been held in Moscow, with the identity of the buyers kept secret.

The assets of Yukos, once Russia's biggest oil group, were auctioned to settle multi-billion-dollar back tax claims filed by the Russian government.

There has been some doubt though as to whether the auction was valid.

The main asset for sale, Yukos Finance, which owned Yukos's foreign assets including a stake in a Slovakian pipeline group, is a Netherlands-based company and lawyers for Yukos claimed the Russian liquidator had no legal right to sell it.

Yukos was declared bankrupt after a government tax fraud investigation in 2003, that was seen as being politically motivated.

The owner of Yukos, former chief executive Mikhail Khodorkovsky, was handed an eight-year prison sentence.