(Adds quotes, context, Rosneft comment)
MOSCOW, July 25 (Reuters) - The quartet of billionaires that owns half of Anglo-Russian oil firm TNK-BP would welcome state oil firm Rosneft as an equal partner, the Interfax news agency reported on Wednesday.
"I don't see any big problem if BP takes the decision to sell its stake in TNK-BP to Rosneft," Interfax quoted one of the shareholders in the AAR consortium as saying.
Rosneft announced on Tuesday that it would enter talks to buy the British oil major's 50 percent stake in TNK-BP, Russia's third-largest oil company. BP put the stake up for sale on June 1 after a breakdown in shareholder relations.
"We (at TNK-BP) have a lot of synergies with Rosneft. I think there is nothing bad in this. TNK-BP's market capitalisation would only grow," the shareholder, who was not named by Interfax, also said.
AAR was not immediately available for comment.
Rosneft's announcement that it would negotiate with BP on the TNK-BP stake, estimated by analysts to be worth $25-$30 billion, signals the determination of the Kremlin to extend its control over the strategic oil sector.
Under a shareholder agreement, BP should hold 'good faith' negotiations with AAR - which groups Mikhail Fridman, German Khan, Viktor Vekselberg and Len Blavatnik - who last week said they were interested in buying half of its TNK-BP stake.
BP may hold talks with other parties but, under the pact, may not strike a deal with anyone else for the next 90 days.
In a statement to Reuters in response to questions, Rosneft said late on Tuesday that it would also be able to work in partnership with AAR should it complete a buyout of BP's stake in TNK-BP.
"Rosneft is certain that, in the event of a transaction, the company will succeed in establishing successful cooperation with the shareholders in AAR," Rosneft said.
"The experience that Rosneft can potentially bring to the JV would promote the development of the existing assets of TNK-BP to the benefit of the interested parties." (Reporting by Douglas Busvine and Olesya Astakhova. Editing by Jane Merriman)