BEIJING >> Chinese and Russian militaries have organized and carried out the ninth joint strategic air patrol in “relevant airspace” over the Sea of Japan on Friday, Chinese state broadcaster CCTV said.

The air patrol was part of an annual cooperation plan between the countries since 2019.

CCTV said the air patrol aims to effectively test and enhance the joint training and operational capabilities of the two air forces.

South Korea’s military said it launched fighter jets after 11 Chinese and Russian military aircraft entered the country’s air defense identification zone (ADIZ). The aircraft lingered over a period of four hours before exiting without incident.

South Korea has protested to China and Russia that the air patrol was conducted without notice.

Countries demand that foreign aircraft entering their ADIZ identify themselves for security reasons. Such zones however do not refer to the territorial airspace of a sovereign state, and often overlap with ADIZs of other countries.

In July, both militaries conducted a joint air patrol using nuclear-capable strategic bombers near the U.S. state of Alaska in the North Pacific and Arctic, prompting the United States and Canada to scramble fighter jets.