BEIJING (Reuters) - Russian and Chinese 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 territorial airspace of a sovereign state, and often overlap with ADIZs of other countries.
South Korea’s military said Friday it scrambled fighter jets as five Chinese and six Russian military planes flew through its air defense zone, an area wider than the country’s airspace.
Five Chinese and six Russian military aircraft entered and exited the Korea Air Defense Identification Zone in the East Sea and South Sea from 9:35 am (0035 GMT) to 1:53 pm, Seoul’s Joint Chiefs of Staff said in a statement.
But the planes crossed into the KADIZ “without violating South Korean airspace”, the JCS said, adding that the military “identified the aircraft before they entered KADIZ and deployed Air Force fighter jets to take tactical measures in preparation for any contingencies.”
An air defense identification zone is a broader area than a country’s airspace in which it tries to control aircraft for security reasons, but the concept is not defined in any international treaty.
China’s defense ministry called the flights “their ninth joint strategic patrol,” which occurred above the Sea of Japan, also known as the East Sea in South Korea.
It added in a post on its official social media account that the flights were held Friday “according to the annual cooperation plan between the Chinese and Russian militaries.”
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.
On October, Russian and Chinese warships carried out anti-submarine firing exercises in the northwestern Pacific Ocean as part of a joint patrol in the Asia-Pacific region. 
The media reported that Russian and Chinese Navy ships begun joint patrols after participating in the Beibu/Interaction 2024 naval exercises in September.