Tokyo: Japanand Australia urged calm on Sunday after Chinese military aircraft locked radar on Japanese fighter jets, a month after the Japanese leader's recent remarks on Taiwan that stirred tensions between Tokyo and Beijing.

Defence Minister Shinjiro Koizumi said Japan formally protested the incident, calling it “an extremely regrettable” act and “a dangerous" one that "exceeded the scope necessary for safe aircraft operations.”

“We have lodged a strong protest with the Chinese side and demanded strict preventive measures,” Koizumi said.

Japan's Defence Ministry said China's military aircraft J-15 took off from the Chinese carrier Liaoning near the southern island of Okinawa on Saturday and “intermittently” latched its radar on Japanese F-15 fighter jets on two occasions Saturday, for about three minutes in the late afternoon and for about 30 minutes in the evening. It was not made clear whether the radar lock incident involved the same Chinese J-15 both times.