MOSCOW, March 14 (Reuters) - Russian aluminium giant Rusal on Friday said it had agreed to buy a 26% stake in an Indian alumina refinery owner for $243.75 million and to acquire up to 50% in stages, a move that should reduce its reliance on third-party raw materials.

Rusal, the world's largest aluminium producer outside China, has not been directly targeted by Western sanctions against Moscow over the conflict in Ukraine, but lost about 40% of its alumina supplies after Australia halted exports to Russia and Rusal shut down its alumina refinery in Ukraine.

To compensate for falling alumina volumes, Rusal increased its purchases of raw materials from China, India, Kazakhstan, and acquired a 30% stake in a Chinese producer in October 2023, reducing the deficit.

As of November 2024, Rusal was still buying more than a third of the alumina it needs for aluminium production on global markets at exchange prices, which it has said "puts serious pressure on production margins".

Rusal agreed to acquire, through a wholly-owned subsidiary, up to 50% of Pioneer Aluminium Industries Limited's share capital in three stages, it said in a statement.

During the first stage, Rusal said it would acquire 26% of Pioneer's shares for $243.75 million plus the amount of appropriate contractual adjustments for net working capital and debt.

"(Pioneer) owns and operates a metallurgical grade alumina refinery located in the state of Andhra Pradesh, India, with nameplate production capacity of 1.5 million tonnes annually," Rusal said.

Rusal and the vendors, Pioneer group of companies and KCap group of companies, plan to supply bauxite and receive alumina from Pioneer pro rata to their respective shareholdings, Rusal said.

Hong Kong-listed Rusal RUAL.MM, 0486.HK on Friday reported a near three-fold jump in its annual earnings, reflecting lower production costs and higher prices for aluminium.

(Reporting by Anastasia Lyrchikova and Alexander Marrow;Editing by Elaine Hardcastle)

((alexander.marrow@thomsonreuters.com;))