A row over BP's dividend looks likely to overshadow the British company's full-year results as Russian shareholders in its TNK joint venture convene on Monday to consider withholding the $1.8 billion payment.

Shareholders in the AAR consortium, which owns the other half of BP's TNK-BP venture, want TNK-BP to remain the prime vehicle of BP's operations in Russia and Ukraine and are seeking a court injunction to halt BP's deal with Rosneft.

A source close to the situation told Reuters on Sunday that AAR's board would convene an extraordinary meeting on Monday to consider withholding the payment of TNK-BP's fourth quarter dividend, due in February.

The source said the board would consider TNK-BP's uncertain prospects in the light of increased competition from Rosneft and the possible need to enhance international expansion.

BP wants to enter fast track arbitration to settle a dispute with Russian shareholders in its TNK-BP joint venture over the British company's shares and exploration deal with Rosneft.

Under the shareholder agreements, the process for settling disputes if they can't be settled within the shareholders is to go to independent arbitration in Sweden, a BP spokesman told Reuters on Sunday.

He said that on Friday BP wrote to the chief executive of TNK-BP, Mikhail Fridman, requesting this arbitration.

If both sides agree to fast track, then that can go ahead quickly. If both sides do not agree it can still go to arbitration, but it can take much longer, he said.

AAR's court case will be heard on February 1 -- the day Rosneft and BP were both due to announce full-year results.

The source also said AAR's lawyers had written to David Peattie, a BP representative on TNK's board, alleging he was in breach of his duties as a director of the joint venture because of his role in negotiations with Rosneft and that TNK-BP was starting legal proceedings against him.

BP would not comment on the matter on Sunday.

Separately on Sunday, a report in The Observer newspaper cited sources close to the U.S. Environmental Protection Agency (EPA) saying the U.S. government was likely to agree to reduce its estimate of the size of the gulf spill, which would cut BP fines.

(Editing by Will Waterman)