China says its air activity was in line with international law.
South Korea on Thursday scrambled fighter jets after Chinese and Russian military planes entered its air defence zone without notice, Al-Jazeera said in a report. There were four Russian and two Chinese fighter jets entered the Korea Air Defence Identification Zone (KADIZ) over the Sea of Japan between 11:53am and 12:10pm (local time) and then departed, the outlet further said. The area of the defence zone wider than the country's airspace. The planes did not violate South Korea's territorial airspace, the military said.
South China Morning Post (SCMP) said that the planes stayed within the air defence zone for 17 minutes, entering from north and flying southeast before exiting KADIZ.
"Our military identified Chinese and Russian military aircraft before they entered the air defence zone, and deployed air force fighter jets to take tactical measures to prepare for contingency situations," the joint chiefs said in a statement.
Reacting to the development, the Chinese foreign ministry said its air activity was in line with international law.
"As I understand it, I believe it is a routine and normal flight activity conducted by Chinese military aircraft in international waters," Chinese foreign ministry spokeswoman Mao Ning was quoted as saying by SCMP.
"It is not something to criticise, and it is also in line with international law," she claimed.
Seoul registered its protest with Beijing about the planes entering its air defence zone without giving any notice. However, it could not contact Russia since the two countries have not established a military communications channel, said the outlet.
What is air defence zone?
It is a demarcated area where a country may unilaterally demand the foreign aircraft to identify themselves to prevent any accidental clash.
Unlike the territorial airspace, there are no international laws that govern air defence zones.
Al-Jazeera said Chinese and Russian warplanes last approached South Korea's airspace in June while conducting joint air force patrols over the Sea of Japan and East China Sea. Seoul had responded by deploying fighter jets in response.