Japan has summoned the Chinese ambassador in Tokyo to express a “serious concern" after a Chinese ship sailed close to disputed islands in the East China Sea.
Tokyo says a Chinese frigate sailed within 38 kilometers of the Senkaku islands shortly after midnight local time on June 9.
Japan administers the uninhabited islands, which China also claims under the name Diaoyu islands.
Japan's Vice Foreign Minister Akitaka Saiki summoned China's Ambassador Cheng Yonghua to lodge a protest.
Reports said the vessel later left the area.
China’s Defense Ministry said it was looking into the reports that one of its navy ships sailed near the disputed islands, adding that its navy had every right to operate in Chinese waters.
Japan is also investigating the presence of three Russian naval ships in the area around the same time.
Chief Cabinet Secretary Yoshihide Suga said officials were analyzing whether the two incidents were coordinated.