The Defense Ministry said Sunday that the Maritime Self-Defense Force spotted an unidentified submarine in the early morning sailing in Japan's contiguous zone south of Minamidaito Island in Okinawa Prefecture.
The submarine, detected by a P-3C MSDF patrol aircraft, was suspected of belonging to the Chinese navy, a government source said. The ministry confirmed the submarine was traveling southeast of the island outside the contiguous zone in the evening.
The ministry has been on alert as an unidentified submarine, thought to be Chinese, was seen sailing in the contiguous zone south of Kume Island on May 13.
Sailing in Japan's contiguous zone, an area outside territorial waters where Japanese law may be applied, poses no problem in terms of international law.