Japan lodged a strong protest with China after a Chinese military aircraft locked its radar on Japanese fighter jets near Okinawa, escalating tensions between the two countries amid already strained relations over remarks by Japan’s prime minister on Taiwan.

Japan’s Defense Ministry said a Chinese J-15 fighter, operating from the aircraft carrier Liaoning, “intermittently” locked its radar onto Japanese F-15 jets twice on Saturday — once for about three minutes in the late afternoon and again for roughly 30 minutes in the evening.

The radar targeting was detected by separate Japanese fighters that scrambled in response to a possible airspace intrusion, though no violation of Japanese territory occurred and no damage or injuries were reported. Officials said it was unclear whether the same J-15 was involved in both incidents.

Defense Minister Shinjiro Koizumi called the radar lock “a dangerous act beyond what is required for safe aircraft operations,” adding that Japan has filed a strong protest and demanded strict measures to prevent a recurrence.

The incident occurred as the Liaoning passed between Okinawa’s main island and Miyako Island while conducting takeoff and landing drills in the Pacific. Japanese jets monitored the Chinese aircraft at a safe distance and avoided provocative maneuvers, according to officials quoted by Kyodo News.

Radar locks are considered serious because the systems can be used to guide missiles. This is believed to be the first case of such targeting between Japanese and Chinese aircraft, though a Chinese warship locked its radar on a Japanese destroyer in 2013.

The confrontation comes weeks after Beijing reacted sharply to Prime Minister Sanae Takaichi’s comments suggesting Japan’s military could intervene if China moved against Taiwan, which Beijing claims as its territory.