BP is in talks with Rosneft that may result in the British oil major acquiring at least 12.5% of the Russian state oil firm, the Kommersant financial daily reported on Thursday, citing sources close to the two companies.

BP's acquisition of Rosneft shares would take place as part of a deal under discussion to sell BP's 50% stake in Anglo-Russian oil venture TNK-BP, Russia's No.3 oil firm.

Rosneft is looking at buying 25% of TNK-BP's shares for $10-$15 billion in cash, with another 25% to be acquired with Rosneft shares, Kommersant wrote.

It also reported that Rosneft planned to use treasury shares representing 9.53% of its equity, as well as shares acquired in a recent buy-back, worth just over 3% of its equity.

Rosneft declined immediate comment on the Kommersant report.

Bankers told Reuters on Wednesday that Rosneft is talking to foreign banks about raising $15 billion in debt financing. A further $5 billion could be raised from Russian banks, one banker also said.

The details published in Kommersant follow a meeting on Tuesday between President Vladimir Putin, Rosneft CEO Igor Sechin, BP's Chief Executive Robert Dudley and Chairman Carl-Henric Svanberg.

Sources close to both companies said on Wednesday that talks were progressing but played down expectations of an imminent breakthrough.

The co-owners of TNK-BP, a quartet of Soviet-born tycoons represented by the AAR consortium, have also expressed interest in buying 25% of the company from BP for $10 billion, but talks have stalled, sources familiar with the matter say.

Under a shareholders agreement, third parties may not strike a deal to buy BP's stake in TNK-BP before a mid-October deadline expires.