Japan has condemned the breach of its airspace by a Chinese military spy plane as “utterly unacceptable,” a day after it scrambled jets and summoned a Chinese embassy official in Tokyo to protest.

At a news conference on Tuesday, Chief Cabinet Secretary Yoshimasa Hayashi described the airspace incursion, which is the first by a military aircraft, as “a serious violation of Japan’s sovereignty” and a threat to national security. On Monday, Japan’s military reported detecting a Chinese Y-9 reconnaissance plane circling above the Danjo Islands, located off the southwestern coast of Kyushu, for approximately two minutes before fighter jets were dispatched to intercept and warn the aircraft to leave.

The Japanese Ministry of Foreign Affairs subsequently summoned acting Chinese Ambassador Shi Yong to express strong objections and demand that China take measures to prevent future violations.

The Chinese embassy has not yet responded to the incident, and no questions were raised about the airspace breach at the Monday press conference held by the foreign affairs ministry.

Hayashi stated that Japan continues to monitor Chinese military activities near its territory and is prepared for any further breaches of airspace. According to Japanese military data, jets were scrambled nearly 669 times between April 2023 and March 2024, with about 70 percent of those incidents involving Chinese military aircraft, though this figure does not include airspace violations.

Japanese defense officials are increasingly concerned about the growing military cooperation between China and Russia, as well as China’s assertive activities in and around Japanese waters and airspace. The two countries are also entangled in a long-standing dispute over the Senkaku Islands, known in China as the Diaoyu Islands. These uninhabited islands and rocks, which have been under Japanese control since 1895, are located about 190 nautical miles (352 kilometers) southwest of Okinawa.