TAIPEI (Taiwan News) — Four aircraft from China’s People’s Liberation Army Air Force (PLAAF) entered Taiwan’s air defense identification zone (ADIZ) Saturday (July 23), according to the Ministry of National Defense.

The military identified the airplanes as two Shenyang J-16 fighter jets, a Shaanxi Y-8 ASW anti-submarine warfare aircraft, and a Shaanxi Y-8 RECCE tactical reconnaissance plane.

As on most previous occasions, the aircraft appeared in the southwest sector of the ADIZ and were soon warned to leave the area. The military also said it deployed air defense missile systems to monitor the activities of the aircraft.

The latest incidents marked the 15th day of PLAAF intrusions for July. They also came amid tension between China and the United States about a visit to Taiwan supposedly planned for August by U.S. House Speaker Nancy Pelosi.