BP prompted the spat with AAR, the consortium of Russian and Russia-connected oligarchs who own half of oil company TNK-BP, by agreeing a share swap and Arctic exploration deal with Russian-state-controlledRosneft <ROSN.MM>.
AAR secured a court injunction that blocked the deal, which finally collapsed in May when the quartet of billionaire shareholders led by Mikhail Fridman refused a $32 billion buyout offer for their TNK-BP stake from BP and Rosneft.
Now AAR is asking a Stockholm-based tribunal to rule on whether the Rosneft deal represented a breach of an exclusivity clause in the TNK-BP shareholder pact that obliges BP to use TNK-BP as its main investment vehicle in Russia.
Minority shareholders in TNK-BP's listed unit, with whom AAR denies any relationship, have filed a separate lawsuit in a Russian court seeking 154.3 billion roubles ($4.9 billion) in damages over the matter.
Sources familiar with the situation said the hearing later on Wednesday was expected to set a schedule for further hearings that would determine whether BP had indeed violated the shareholder agreement and was liable for damages.
A BP spokesman on Wednesday repeated earlier denials that AAR or minority shareholders in TNK-BP had suffered as a result of BP's decision to try to do the deal with Rosneft.
BP has argued that Rosneft would not have chosen TNK-BP as a partner since it lacked offshore drilling expertise.
AAR and BP both declined comment on the arbitration hearing, whose proceedings are confidential. The hearings are usually held by phone or in London legal chambers.
In a separate development, the Kommersant business daily reported on Wednesday that BP had frozen talks on a deal to sponsor a high-tech hub championed byPresident Dmitry Medvedev and chaired by Viktor Vekselberg, a TNK-BP shareholder.
The report that BP had put on ice talks on the 6.7 million pound ($10.5 million) sponsorship of the Skolkovo innovation project came after Medvedev last weekend said he would cede Russia's highest office to Prime Minister Vladimir Putin.
A spokesman for BP in Moscow said the British oil major was "still interested in the project, but its implementation depends on the agreement of some details with all the parties involved." ($1 = 0.637 British Pounds)
(Additional reporting by Douglas Busvine and Vladimir Soldatkin in Moscow; Editing by Helen Massy-Beresford)