Prime Minister Shinzo Abe's plans to expand Japan's noncombat role in armed conflicts beyond "areas around Japan" could see Tokyo becoming dragged into action in the South China Sea in support of U.S. forces, government and ruling party sources say.

Abe will send legislation to the Diet next month — with the backing of coalition partner Komeito virtually assuring its passage — allowing Japan to ship fuel and ammunition to American units anywhere, should Tokyo judge its national security to be at stake.

Japan and the United States have no territorial claims in the energy-rich South China Sea, but tensions are rising between China and the Philippines in the strategic waterway where some $5 trillion in ship-borne trade passes every year, much of it heading to and from Japanese ports.