A new aerial incident has worsened already tense relations between Japan and China, after Tokyo accused Chinese fighter jets of using fire control radar to "jam" Japanese F-15 jets in airspace near Okinawa.

Japanese Prime Minister Shinzo Abe said Japan would “respond calmly and resolutely” to the incident, promising strong measures to increase maritime and air surveillance. The Foreign Ministry summoned China’s ambassador to Tokyo on Sunday. Beijing, for its part, rejected the accusations and lodged its own formal protests. According to Japan’s Defense Ministry, J-15 jets launched from the Chinese aircraft carrier Liaoning used their fire control radar twice against Japanese F-15 jets, at 16:32 p.m. and about two hours later on Saturday. The incident occurred southeast of Okinawa, where China said it was conducting “distance maritime exercises.”

The Japanese ministry also reported about 100 sorties from the Liaoning over the weekend. Although there were no injuries or damage, Tokyo called the incident “extremely dangerous.” Radar “lock” is one of the most threatening actions in military aviation: the radar stops its general scan and locks on to a single target, suggesting the possibility of an attack. This forces the targeted aircraft to take evasive maneuvers.

According to the Japanese news agency Kyodo, it is the first time Tokyo has reported such an incident involving Chinese fighter jets. Defense Minister Shinjiro Koizumi called the action “dangerous and extremely regrettable.” Tensions remain high as the two countries exchange diplomatic protests and continue military patrols in one of the most sensitive areas of the Indo-Pacific.