TOKYO (Reuters) - Japan scrambled fighter jets to prevent possible incursions by Chinese planes a record high number of times for the July-September period, the Defence Ministry said on Monday, with Tokyo and Beijing at loggerheads over disputed islets.

Japan jets scrambled 117 times, up from 103 in the same period of last year, although it was lower than the all-time high of 164 times recorded in the final quarter of 2014.

It was not immediately clear why the number of scrambles rose and the ministry did not offer an explanation.

Japan has long been mired in a territorial dispute with China over a group of tiny, uninhabited East China Sea islands, called the Senkaku in Japan and Diaoyu in China.

Patrol ships and fighter jets from Asia's two biggest economies have been shadowing each other on and off near the islets, raising fears that a confrontation could result in a clash.

Japanese Prime Minister Shinzo Abe and China's top diplomat, Yang Jiechi, last week agreed to push for early adoption of a communication mechanism, now in the works, to avert misunderstandings between their militaries.

Sino-Japanese ties, also plagued by the two countries' wartime past, concerns over Tokyo's bolder security stance and Beijing's increasing military assertiveness, have thawed a little in the last year.

Scrambles against Russian planes fell 43 percent from a year earlier to 51 times in July-September, helping bring down the number of Japan's overall scrambles in the three-month period by 12 percent to 170.

Russian bombers and patrol planes often fly close to Japan's northern air space close to Hokkaido and four smaller islands claimed by both countries.

(Reporting by Kiyoshi Takenaka; Editing by Nick Macfie)