* Binding deal to be signed in coming days - sources
* AAR has had rocky relations with Rosneft
MOSCOW Dec 11 Russian oil group Rosneft will announce within days it has finalised a deal to buy half of domestic peer TNK-BP from AAR for $28 billion, several sources familiar with the situation said.
Rosneft and AAR declined to comment.
Last month, Rosneft head Igor Sechin said it and AAR - a consortium of four Soviet-born tycoons - should sign a binding agreement in December.
In October, Rosneft signed a memorandum of understanding to buy AAR as part of a $55 billion takeover in which it will also acquire British group BP's 50 percent stake in TNK-BP, Russia's third-largest oil company.
The BP leg of the deal, already approved at board level and by the government, should close in the first half of 2013, but a timetable for the agreement with AAR had not been outlined.
Investors have been watching the part of the deal with AAR, which represents Len Blavatnik, Mikhail Fridman, German Khan and Viktor Vekselberg, and which has had rocky relations with Rosneft.
Last year, the consortium won an injunction blocking Rosneft's attempt to tie up with BP and tap Russia's Arctic hydrocarbon riches. The deal was abandoned after an arbitration panel found it violated TNK-BP's shareholder agreement.
Last month, AAR and BP agreed to end the legal battles that had blighted their decade-old partnership, paving the way for the deal with Rosneft.