Posco, the world's fourth largest steel maker by output, is moving to boost its investments in Australia's resources assets, saying Friday it is acquiring a stake in iron ore maker AMCI (WA) Pty Ltd. and boosting its stake in Murchison Metals Ltd. as part of its effort to secure key raw materials.

The South Korean steel maker said in a statement it will invest 194.7 billion won ($162 million) to acquire a 49% stake in AMCI (WA) Pty Ltd. Through the acquisition, Posco will have a roughly 25% stake in the Australian Premium Iron, or API, project, which is being developed by a 50-50 joint venture set up between Australian miner Aquila Resources Ltd. and AMCI parent American Metal & Coal International.

Posco said it expects to secure 9.8 million metric tons of iron ore from the API mine each year from 2014, and the acquisition will help boost the steel maker's iron ore self-sufficiency ratio to 34% from 18% currently. Iron ore is a raw ingredient for making steel.

Posco's deals continue the flood of investment in Australia's booming resource sector from Asia as customers look to lock in supply amid still-strong demand for commodities including coal and iron ore from the region. Posco already has made several investments in Australian resources companies, including an 8.3% stake in Macarthur Coal Ltd., a stake of close to 20% in Sandfire Resources N.L. and a near-15% stake in Cockatoo Coal Ltd.