Chinese aircraft said undetected by Japanese radar TOKYO, Dec. 17 (UPI) -- Japanese defense radars have failed to detect Chinese aircraft entering airspace over the disputed Senkaku Islands, a Japanese defense official said. Japanese Defense Minister Satoshi Morimoto said radar systems failed to detect the intrusion of a Chinese airplane Thursday near the disputed Senkaku Islands in Okinawa Prefecture. In light of the incident the Japanese government plans to increase the level of alert around the islands. "Considering China's claim that the airspace is part of Chinese territory, the nation apparently is trying to emphasize its sovereignty over the Senkaku Islands," Defense Minister Satoshi Morimoto said last week. It's very regrettable. The Japanese Ministry of Defense said the radar system failed to track the Chinese aircraft due to a lack of coverage. Japanese Joint Chief of Staff Gen. Shigeru Iwasaki, appearing at a news conference, said fixed radar systems had been deployed in "a limited number of locations" in Okinawa Prefecture and airborne warning systems were ordered to supplement to radar. Most of Japan's ground and aircraft radar systems are manufactured by Mitsubishi Electric, Japan's second-largest defense contractor behind Mitsubishi Heavy Industries Ltd. Both China and Japan claim the Senkaku Islands.