The world's biggest miner BHP Billiton said it has sold a 15 percent stake in one of its key iron ore mines in Australia to two Japanese conglomerates for US$1.5 billion.

Itochu Corp. agreed to buy an eight percent holding in the Jimblebar mine in the resource-rich Pilbara region of Western Australia for US$800 while Mitsui will pay $US700 million for a seven percent stake.

The Jimblebar mine is wholly-owned by BHP and will have initial production capacity of 35 million tonnes of the steelmaking commodity per annum, rising to 200 million tonnes per annum when fully operational.

Itochu and Mitsui already collectively own 15 percent of BHP's mine, railway and port infrastructure in the region.

"We are pleased to extend our successful, long-standing joint venture relationship with Itochu and Mitsui," BHP's iron ore president Jimmy Wilson said.

Australia's Foreign Investment Review Board has to approve to the transaction, with the deal expected to be signed off during the September quarter.