Japan is considering deploying Aegis destroyers near the West Sea to deal with the long-range missile threat from North Korea. The warships have state-of-the-art electronics equipment and missile systems and radar that can track an aircraft flying 1,000 km away.

Japan has six Aegis destroyers each costing up to 140 billion yen (around W2 trillion).

Japan’s Defense Ministry in a recent report said it is mulling plans to deploy the ships when there is a warning that North Korea will fire a long-range missile to “waters surrounding the launch site,” the Asahi Shimbun reported Wednesday. That can only mean the high seas near the West Sea. Although it is possible under international laws for military vessels to patrol the high seas, no Japanese Aegis destroyer has ever approached areas near the West Sea.

The South Korean government’s official position is that Japan has the right to deploy Aegis destroyers on the high seas and the matter does not require consultation with Seoul. But there are concerns within the government that the move may be an excuse to expand the operating sphere of Japan’s Self-Defense Forces.

“There are suspicions that Japan is trying to expand the operating area of its Aegis destroyers to the West Sea using North Korea’s missile threat as an excuse,” said one diplomatic source here. Aegis destroyers are capable of monitoring objects 1,000 km away and therefore do not need to approach so close for such surveillance activities.

Some expect the issue to be brought up during the Asia Security Summit or Shangri-La Dialogue in Singapore on Friday, where the defense chiefs of South Korea, China and Japan meet. China may also object. Beijing strongly protested against a major South Korea-U.S. naval drill in the West Sea in 2010 involving American aircraft carriers.