South Korea said it had scrambled its fighter jets in response to an incursion into its air defense identification zone on Thursday. Four Russian and two Chinese aircraft crossed into the Korea Air Defense Identification Zone (KADIZ) over the Sea of Japan, also known as the East Sea, between 11:53 am (02:53 GMT) and 12:10 pm (03:10 GMT) on Thursday and then departed, South Korea’s Joint Chiefs of Staff (JCS) said in a statement.

But "there was no invasion of airspace," the joint chiefs added, and the South Korean military identified the planes "before they entered KADIZ, and deployed air force fighter jets to take tactical measures in preparation for contingencies."

According to the International Civil Aviation Organisation, an air defense identification zone is not territorial airspace, but countries can set them up to call on foreign planes entering the area to identify themselves to prevent accidental clashes.

That differs from a nation’s airspace, which usually means the space above its territory, extending 12 nautical miles away from its coastline.

The Chinese foreign ministry said China’s air activity was in line with international law.

Unlike airspace, there are no international laws that govern air defense zones.

“As I understand it, I believe it is a routine and normal flight activity conducted by Chinese military aircraft in international waters,” said Chinese Foreign Ministry spokeswoman Mao Ning.

“It is not something to criticize, and it is also in line with international law.”

China and Russia are North Korea's traditional allies, and Washington warned last month that military ties between Pyongyang and Moscow were "growing and dangerous."

In June, four Chinese and four Russian military aircraft passed through the southern and eastern parts of the zone during a joint air force patrol operation, which prompted the South Korean and Japanese militaries to scramble their fighter jets.

Since 2019, China and Russia have been conducting joint drills including the dispatch of jets once or twice a year eastward of the air defense zone. Beijing has never informed Seoul in advance of the movements of its military planes.

Image source: AFP