TAIPEI (Taiwan News) — The defense ministry detected 21 Chinese military aircraft and seven naval vessels around Taiwan between 6 a.m. on Friday and Saturday.

Thirteen of the aircraft reportedly crossed the median line of the Taiwan Strait and entered the nation’s northern and southwestern air defense identification zone, or ADIZ. In response, Taiwan sent aircraft and naval ships and deployed coastal-based missile systems to monitor Chinese activity.

In August so far, Taiwan has tracked Chinese military aircraft 279 times and ships 114 times. Since September 2020, Beijing has increased its use of “gray zone tactics” by operating military aircraft and naval vessels around Taiwan.

CSIS defines gray zone tactics as “an effort or series of efforts beyond steady-state deterrence and assurance that attempts to achieve one’s security objectives without resort to direct and sizable use of force.”