South Korea has lodged a complaint with the Chinese and Russian defence attaches based in the country, a day after their warplanes entered its air defence zone.
Seoul said it sent up fighter jets to "take tactical measures in preparation for any emergencies" after seven Russian and two Chinese military aircraft "briefly entered" the zone on Tuesday, but noted they "did not violate" South Korea's airspace.
Some countries delineate air identification defence zones, wherein they require foreign planes to identify themselves. These are not part of sovereign airspaces under international law.
In March this year, Seoul also deployed fighter jets after several Russian warplanes flew into the zone.
The Russian aircraft entered Korea's Air Defense Identification Zone (Kadiz) near Ulleung Island and Dokdo, while the Chinese aircraft entered near Ieodo, a Joint Chiefs of Staff official said, according to South Korean media.
