The intrusion of two Japanese reconnaissance aircraft into a China-Russia joint navy exercise is against international law and can make the already volatile relations between China and Japan more complicated, analysts said.
China and Russia conducted a weeklong naval exercise in the East China Sea, which officially concludes on Monday, and issued no-fly notices days before the exercise. However, a Japanese OP-3C surveillance plane and a YS-11EB electronic intelligence aircraft intruded into the airspace of China's East China Sea Air Defence Identification Zone on Saturday morning where the exercise was being held.
China reportedly had to deploy two SU-27s to intercept the intruders.
On Sunday, the Ministry of National Defence criticised Japan for the move, saying it seriously violated international law and globally accepted norms, and "could have easily caused a misunderstanding and even led to a mid-air accident".
Zhang Junshe, a researcher at the PLA's Naval Military Studies Research Institute, said Japan often sends military vessels and aircraft to interfere in the training of the Chinese navy at close quarters, "which has posed a huge disturbance".
Observers also said Japanese defence authorities have hyped the technical details in the latest airspace confrontation, which claimed the Chinese jet fighters flew dozens of meters from the Japanese aircraft, while they deliberately shied away from the fact that Japan's military aircraft were "doing something wrong".
Tokyo should stop its act, "otherwise Japan will bear all consequences from this", the Chinese defence ministry said.
The Chinese military aircraft are entitled to safeguard the country's airspace security and exercise necessary recognition and precautions toward external aircraft that enter the Chinese ADIZ, it said.
Early in 2010, Chinese Ambassador to Japan Cheng Yonghua criticised Japan's reconnaissance as "running against the spirit of mutual understanding and mutual trust".
During the China-Russia naval drill last July, Japan dispatched aircraft and vessels to closely trail the Chinese warships, according to Du Wenlong, a senior researcher at the PLA's Academy of Military Science.
Jiang Xinfeng, another researcher at the academy, said Japan's defence policies toward China are becoming explicitly coercive and even confrontational.
Tokyo "has overreacted to and misinterpreted" the growth of China's national defence capabilities, Jiang said.