Russia's Tyumen arbitration court on Friday ordered BP PLC to pay just over 100 billion rubles ($3.1 billion) in damages to TNK-BP, a ruling that the British company called a "corporate attack." The court ruling is to take effect in 30 days unless appealed, in which case it would become effective at the end of the appeal process, BP's lawyer said
Russia's Tyumen arbitration court on Friday ordered BP PLC to pay just over 100 billion rubles ($3.1 billion) in damages to TNK-BP, a ruling that the British company called a "corporate attack."

The court ruling is to take effect in 30 days unless appealed, in which case it would become effective at the end of the appeal process, BP's lawyer said.

"We will challenge today's ruling in accordance with the procedure established by the law, and expect that the court of appeal will adopt a reasonable and fair decision," BP said in a statement. "We consider this claim as an attempted corporate attack and believe that today's ruling should be cancelled."

Friday's ruling comes amid rising tensions between BP and its partners in the 50-50 TNK-BP venture, a group of Soviet-born billionaires known as AAR. Earlier this week, BP said it was in talks to sell its stake in TNK-BP to OAO Rosneft, a move that analysts said could put pressure on AAR, which is also bidding for the stake.

Friday's ruling could further complicate sales talks.

The decision "may somehow make AAR's position stronger because BP faces these legal issues but this is not the final word," said Ildar Davletshin, an oil and gas analyst at Renaissance Capital.

AAR and TNK-BP declined to comment. Rosneft had no immediate comment.

Lawyers for Mr. Prokhorov, who owns a very small stake in TNK-BP's Russian-listed unit, have argued that BP had done damage to the joint venture when last year it sought an alliance with OAO Rosneft, the state oil company, without involving TNK-BP. BP's Russian partners blocked that alliance in separate legal proceedings in the U.K. and are seeking damages from BP through arbitration.

BP says the damage claims are groundless.

Although the payment ordered by the court is less than the RUB288 billion original claim, "the decision is still a positive one," said Mr. Prokhorov's lawyer, Dmitry Chepurenko. "The court has acknowledged that the truth is on our side."

In 2011, Rosneft and BP almost bought out AAR's stake in TNK-BP for around $32 billion, but the deal fell through, thwarting BP's plans for a landmark Arctic oil exploration alliance with Rosneft and poisoning already-tense relations with AAR.

In recent weeks, Russian officials have said they would not like to see BP, one of the biggest foreign investors in the oil sector, leave Russia entirely. Some analysts have suggested a TNK-BP sale could become the first step in a broader alliance between BP and Rosneft, possibly along the lines of the Arctic deal discussed last year.