Japan, in the midst of a land dispute with China, scrambled fighter jets to prevent possible incursions by Chinese planes a record number of times from July through September, the Defense Ministry said on Monday.
Japan jets scrambled 117 times, up from 103 in the same three-month period of last year, although it was lower than the all-time high of 164 times recorded in the final quarter of 2014, Reuters reported.
However, it is unclear why the number of scrambles rose and the ministry did not offer an explanation.
Japan and China are at odds over ownership of a group of tiny, uninhabited islands in the East China Sea, called the Senkaku in Japan and Diaoyu in China. Patrol ships and fighter jets from the two countries have been shadowing each near the islets, raising fears of a conflict.
The countries are now working on a communication system aimed at averting misunderstandings between their militaries.
Ties between Japan and China have long been troubled by their wartime history. But relations have improved slightly in the past year, despite Tokyo's bolder security stance and Beijing's increasing military assertiveness.
Scrambles against Russian planes fell 43% from a year earlier to 51 times in July-September, helping to bring down the number of Japan's overall scrambles in the three-month period by 12% to 170, Reuters reported.
Russian bombers and patrol planes often fly close to Japan's northern air space and four smaller islands claimed by both countries.