Russia\'s state oil giant Rosneft said on Tuesday it had opened talks with the British energy group BP on acquiring a stake in the troubled but lucrative TNK-BP joint venture it co-owns with four tycoons. The announcement follows weeks of denials by Russia\'s largest oil company of any ownership interest in a venture that has grown into the country\'s fourth largest crude producer since being formed in 2003. BP said on June 1 that it was seeking buyers for its 50 percent stake in TNK-BP because of continuing boardroom disputes with the powerful billionaires who jointly operate the company. \"Rosneft announces that, in connection with BP\'s recent statements regarding its intention to pursue a potential sale of its participation in TNK-BP, Rosneft has informed BP of Rosneft\'s interest in a potential acquisition of such participation,\" the company said in an English-language statement. \"As a result, the parties agreed to commence negotiations on this matter and signed a non-disclosure agreement.\" Rosneft said it had also informed the tycoons who operate their stake in TNK-BP through the Alfa Access Renova (AAR) consortium of their interest in BP\'s stake. The state firm did not disclose the size of the stake under discussion. AAR announced last week that it had opened negotiations on acquiring half of BP\'s shares in the joint venture. The TNK-BP shareholders\' agreement gives the tycoons three months to negotiate a deal with BP first but does not keep the British firm from holding talks with other interested parties.