BEIJING China's Defence Ministry said on Thursday it has lodged a formal diplomatic complaint over what it called "dangerous provocation" by Japan for shadowing Chinese military exercises in the western Pacific.
Sino-Japanese ties have been strained for months by a dispute over tiny islands in the East China Sea believed to be surrounded by energy-rich waters. They have also been overshadowed by what China says is Japan's refusal to admit to atrocities committed by Japanese soldiers in China between 1931 and 1945.
Defence Ministry spokesman Yang Yujun said that a Japanese naval and air patrol disrupted a Chinese live ammunition military drill last Friday, without giving the precise location.
Yang also said Japanese patrols of ships and aircraft were gathering information about the exercises.
"Not only did this interfere with our normal exercises, but endangered the safety of our ships and aircraft, which could have led to a miscalculation or mishap or other sudden incident," Yang told a news briefing.
"This is a highly dangerous provocation, and China's Defence Ministry has made solemn representations to the Japanese side," he added, according to a transcript of his remarks on the ministry's website.
Diplomatic complaints are normally lodged by the Foreign Ministry, so the Defence Ministry's unusual move signals the military's anger.
A former Japanese military officer told Reuters this week that the situation in the East China Sea was worrisome.
"As the Chinese are getting more active, we have more opportunities to confront each other," he said. "If something happens accidentally, it may very seriously deteriorate the bilateral relationship."
Ties between the two countries took a hit in September 2012 after Japan bought two of the disputed islets from a private owner, setting off a wave of protests and boycotts of Japanese goods across China.
China on Saturday criticised a Japanese media report saying Prime Minister Shinzo Abe had approved a policy for Japan to shoot down foreign drones that ignore warnings to exit its airspace.
Abe has said Japan is ready to take a more assertive stance towards China.
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