North Korea threatened Saturday to shoot down any Japanese planes that enter its airspace, accusing Tokyo of spying near one of its missile launch sites. Pyongyang had designated a no-sail zone off its eastern coast from June 25 to July 10 for military drills, raising concerns that it might test-fire short- or mid-range missiles in the coming days, in violation of a UN resolution. North Korea's air force said Japanese E-767 surveillance aircraft conducted aerial espionage near the Musudan-ri missile site on its northeast coast Wednesday and Thursday. The country's official Korean Central News Agency said the air force "will not tolerate even a bit the aerial espionage by the warmongers of the Japanese aggression forces but mercilessly shoot down any plane intruding into the territorial air of the (North) even 0.001 mm." An official from Japan's defense ministry said the country's planes regularly gather information on North Korea, but declined to comment on the types of planes used or the locations monitored. He spoke on condition of anonymity, citing government policy. The threat against alleged Japanese aerial espionage is rare, though the North has regularly complained of US spy missions in its airspace. Japan is very sensitive to North Korea's missile programs, as its islands lie within easy range. In 1998, a North Korean missile flew over Japan's main island. Tokyo has since spent billions of dollars on developing a missile shield with the United States and has launched a series of spy satellites primarily to watch developments in North Korea. But in April, another rocket flew over Japan's main island, drawing a strong protest from Tokyo. Pyongyang claims it put a satellite into orbit; however the US and its allies said the launch was really a test of the country's long-range missile technology. The launch was one of a series of missile tests in recent months, and the communist regime further raised tensions by conducting a second underground nuclear test in May. Its actions have drawn harsh international condemnation and new UN sanctions. Over the weekend however, a US official said the United States would not use force to search the Kang Nam, a North Korean ship headed for Myanmar and suspected of carrying munitions. The statement effectively meant - at least regarding the Kang Nam - that the United States would not enforce the recent UN resolution against Pyongyang.