The U.S. is planning a major expansion of missile defenses in Asia, a move American officials say is designed to contain threats from North Korea, but one that could also be used to counter China's military.

The planned buildup is part of a defensive array that could cover large swaths of Asia, with a new radar in southern Japan and possibly another in Southeast Asia tied to missile-defense ships and land-based interceptors.

It is part of the Obama administration's new defense strategy to shift resources to an Asian-Pacific region critical to the U.S. economy after a decade of war in Iraq and Afghanistan.

The expansion comes at a time when the U.S. and its allies in the region voice growing alarm about a North Korean missile threat. They are also increasingly worried about China's aggressive stance in disputed waters such the South China Sea, where Asian rivals are vying for control of oil and mineral rights.

U.S. defense planners are particularly concerned about China's development of antiship ballistic missiles that could threaten the Navy's fleet of aircraft carriers, critical to the U.S. projection of power in Asia.