Japan Coast Guard patrol boat crews spotted aircraft that may have been unmanned Chinese drones near the disputed Senkaku Islands in the East China Sea in mid-December 2012 and again in late June, Japanese government sources said Tuesday.
Japan's Defense Ministry did not make a public announcement at the time due to a lack of evidence the aircraft were drones and that they came from China, the sources said.
Japan's Defense Ministry and the coast guard have since tightened their air surveillance in the area, suspecting the possibility that China's military might have intended to test Japan's air defense capabilities.
On Monday, the ministry's Joint Staff Council said an airplane believed to be a drone flew near the uninhabited islets, prompting Japan's Air Self-Defense Force to scramble its jetfighters.
This time, the Defense Ministry was able to photograph the drone and decided to release the information to the media, the sources said, noting that China's armed forces might have been flying such planes near the Senkaku Islands for some time.
One Japanese government source said the fact that the drone flew during daytime could suggest China's military might have stepped up its activities.
Japan Coast Guard officers spotted what seemed to be two unmanned aircraft in the early hours of Dec. 15, two days after an aircraft belonging to the China Marine Surveillance intruded into Japan's airspace near the Senkaku Islands for the first time.
The officers spotted the two aircraft believed to be drones flashing lights some 50 kilometers off Kuba Island, one of the Senkaku islets, the sources said.
The aircraft spotted then were believed to be unmanned because they did not respond to calls from the coast guard patrol ships and were not transmitting signals distinctive to manned aircraft.
There was a similar case in late June in an area closer to the Senkaku Islands than in the December 2012 incident.
The drones may have been China's BZK-005 high-altitude long-range unmanned reconnaissance aircraft capable of flying for 40 hours without refueling, the sources said.
In September last year, the Japanese government bought some of the islands from a private owner to place them under state control.
The territorial dispute over the uninhabited islands subsequently intensified with China, which calls them Diaoyu, repeatedly sending ships to the Japanese waters around the islets.
Taiwan also claims the Senkaku group which it calls Tiaoyutai.