Japan and China have traded accusations after China scrambled fighter jets when Japanese military aircraft entered an air defence zone declared by Beijing over the East China Sea.
China's defence ministry said on Sunday that two Japanese planes entered the defence zone the previous day during a joint military drill with the Chinese and Russian navies.
A ministry statement demanded that Japan stop all reconnaissance and interference activities.
"Japanese military planes intruded on the exercise's airspace without permission and carried out dangerous actions, in a serious violation of international laws and standards, which could have easily caused a misunderstanding and even led to a mid-air accident," the statement said.
China declared its air defence zone last year despite protests by Japan and the United States.
According to Tokyo's defence ministry, a Japanese surveillance aircraft OP-3C was approached closely by a Chinese fighter jet on the same day.
Shortly after, Tokyo claimed that another Chinese fighter jet came as close as 30 metres to another Japanese aircraft, the AP news agency reported.
"This time, it is completely out of ordinary that they came so close to our aircraft which was flying over the international sea. I really think this was totally out of line action," said Itsunori Onodera, Japanese defence minister.
Onodera added that his country had notified China about what happened.
China and Russia started joint naval exercises on Tuesday as their leaders promised to strengthen relations in the face of international criticism over their territorial disputes, the AFP news agency reported.
The exercises ended on Sunday.
Tensions between China and its neighbours have also risen sharply in the South China Sea in recent weeks, following the deployment of a Chinese oil rig in waters also claimed by Vietnam.