Japan says it will file a protest with the Chinese government after one of its submarines intruded into Japanese territorial waters.
Japan's chief government spokesman Friday identified the submarine that intruded into Japanese territorial waters earlier this week as being from China - as had been suspected.
Hiroyuki Hosoda says Tokyo, through diplomatic channels, will soon lodge a protest with Beijing about the incident.
Defense Agency Director General Yoshinori Oda has ordered the Maritime Self Defense Force to stop pursuing the submarine after it moved outside a zone where Japan's military can operate freely.
For the first time in five years, Japanese naval force went on alert Wednesday, after the submarine spent two hours in waters near the southern Okinawan islands. When first spotted, the sub was near an offshore gas project in disputed waters between the two Asian nations.
Japanese officials have said sounds made by the vessel's propeller were that of a Chinese military Han-class nuclear powered submarine.
As late as Thursday, Chinese officials shrugged off suspicions that the submarine was one of theirs - saying they did not know anything about it.