Russian SU-35 fighter jets (near Moscow in 2017)
Photo: Sergei Karpukhin/ REUTERS
Two Chinese and six Russian warplanes entered the country's air surveillance zone on Wednesday, according to South Korea.
South Korea then launched its own jets, the military staff in Seoul said.
South Korea's actual airspace was not violated.
According to the information, early in the morning Chinese H-6 bombers repeatedly penetrated the KADIZ air defense zone, which supplements South Korea's airspace as a kind of buffer zone.
A few hours later, they were escorted by Russian jets, including TU-95 bombers and SU-35 fighter jets.
According to the Russian news agency Ria Novosti, the Ministry of Defense in Moscow said that the planes acted in accordance with international law and did not violate the airspace of other countries.
The flights were part of joint patrols over the Sea of Japan and the East China Sea, Russian media report, citing the Defense Ministry.
Moscow does not recognize the air defense zone
An air defense zone is an area where countries require foreign aircraft to identify themselves by special measures.
Unlike a country's airspace, the space above its territory and territorial waters, there are no international rules for air defense zones.
Moscow does not recognize South Korea's air defense zone.
Beijing said the zone is not a territorial airspace and all countries should enjoy freedom of movement there.
There have recently been several incidents in the region.
The South Korean military said it deployed fighter jets in early November after spotting about 180 North Korean fighter jets near the border.
The North Korean aircraft were flying north of the so-called tactical measurement line, which runs up to 20 kilometers north of the military demarcation line (MDL).
South Korea deployed 80 aircraft in response, including F35 stealth jets.
An incident involving ten North Korean fighter jets had already led to Seoul sending out fighter jets in October.