Tokyo (AsiaNews/Agencies) – Japan's Defence Agency announced that Japanese fighter jets scrambled 13 times in 2004 in response to Chinese military aircrafts approaching their airspace.

A Defence Ministry spokeswoman said that such incidents involving what were believed to be reconnaissance planes were up from just two in 2003, but declined to provide further details.

What is certain is that although there were no clashes between the planes, the incidents have increased tensions between Beijing and Tokyo.

The Japanese government announced that it would "monitor possible violations of its air space" and "defend its sovereign rights", including those over the disputed Diaoyu Islands in the East China Sea.

The Diaoyu or Senkaku Islands (in Japanese) have been a bone of contention between Tokyo and Beijing for some time.

On April 12, 2005, Japan authorised private companies to start natural gas exploration on the seabed around the islands.

China called the decision a "grave provocation" and warned Japan that by continuing to claim sovereignty over the islands it will cause relations between the two countries to "badly deteriorate".

Tensions between Beijing and Tokyo are rising because both sides are searching for energy sources, but also because of Japan's historical revisionism and its quest for a permanent seat on the Security Council of the United Nations.