BP must pay its joint venture TNK-BP $3bn (£1.8bn) in damages over an aborted deal to partner Russia's state oil firm Rosneft in an Arctic exploration, a Siberian court has ruled.

The ruling against the oil giant, which it will appeal against, led to the company's lawyer saying the reputation of the Russian judiciary was severely damaged.

The company is desperately trying to leave Russia and has put its 50% stake in TNK-BP up for sale, with Rosneft the only company to confirm it is interested in buying the entire stake, worth up to $30bn.

The Siberian case was bought by minority shareholder, Andrey Prokhorov, who has claimed a linkup between Rosneft and BP damaged the value of TNK-BP, which is a 50:50 partnership with the London-based firm and a group of Russian oligarchs, Alfa Access-Renova (AAR).

The fine was announced as TNK-BP reported net profits in the last three months had fallen by over 60% to $808m, from $2.2bn a year ago.

It is the fourth court case brought by Prokhorov, after his first case where he claimed $16bn damages was thrown out last year. He twice appealed to higher courts in Russia and eventually had the case referred back to the original Tyumen arbitration court, which has now ruled that $3bn damages be paid to TNK-BP.

The decision comes less than a month after AAR said it would be interested in buying half of BP's stake in the venture for $10bn, made up of $7bn cash and $3bn from an agreement to waive a lawsuit over the Rosneft partnership.

A spokesman for BP said: "We consider the court decision as unjustified. Today's ruling will be challenged in the court of appeal. All the plaintiff's arguments are based on absurd assumptions, and are not related to either the company's interests, or the interests of its shareholders.

"TNK-BP did not suffer and could not have suffered any damages; any arguments on the issue are pure speculation. TNK-BP initially was not considered as possible participant in the Arctic projects by Rosneft. We consider this claim as an attempted corporate attack and believe that today's ruling should be cancelled."

BP's lawyer, Konstantin Lukoyanov, added: "The court award seriously damages the reputation of the Russian legal system and its ability to protect the rights of bona fide investors from illegal corporate attacks."

Animosities between BP and AAR over TNK-BP started last year when Rosneft and BP announced a joint venture to start Arctic exploration.

Rosneft was to receive 5% of BP's shares, worth $7.8bn, and BP 9.5% of Rosneft's shares.

However, AAR secured an injunction stopping the deal after arguing that it breached the TNK-BP shareholder agreement that said future Russian opportunities must be pursued together.

BP tried to buy out AAR last year for $32bn, with Rosneft as its partner, but the deal fell apart at the last minute.

It is currently in a 90-day buyout period where it will hold negotiations with both AAR and Rosneft to agree a deal.

Earlier this week Russian news agency Interfax reported one AAR shareholder saying: "I don't see any big problem if BP takes the decision to sell its stake in TNK-BP to Rosneft."