Itochu Corp, Japan's fourth-biggest trading house, said on Monday it planned to triple its equity stakes in overseas iron ore mines to 30 million tonnes a year by 2015 as it sees tightening demand.

    Planned expansions of iron ore output facilities at a joint venture with BHP Billiton in Australia, among other steps, will boost Itochu's holdings to 25 million tonnes, while it aims to add 5 million more through new acquisitions, Yoichi Kobayashi, Itochu's senior managing director, told a news conference.

    "We aim to aggressively tap upstream operations, including exploration, in the metal business, an area where we are relatively weak compared with other trading houses," he said.

    Itochu is bidding for Brazilian iron ore miner Namisa in a deal that could be worth as much as $10 billion jointly with Japan's top five steelmakers, including Nippon Steel Corp, according to sources familiar with the bidding.

    Among Japanese trading houses, Mitsui & Co now owns iron ore mine equity stakes equivalent to about 44 million tonnes a year.

    Itochu expects iron ore prices to stay firm as supplies from India and China may be limited while numerous steelmakers are planning new blast furnaces in Brazil, India, Vietnam and other emerging economies.

    Itochu said it also planned to double its holdings in overseas coal assets to 15 million tonnes by 2015, while tripling its stakes in aluminium assets to 570,000 tonnes, Kobayashi said.