Eleven Chinese and Russian military aircraft entered South Korea’s air defense identification zone on Friday over a period of four hours, prompting South Korea to launch fighter jets.

Axar.az reports that citing Reuters, the Russian and Chinese aircraft entered the area in sequence, all exited without incident or intruding South Korea’s airspace, the Joint Chiefs of Staff said in a message to reporters.

South Korea’s military had identified the aircraft before they entered the zone and deployed air force jets which conducted tactical maneuvers in response, it said.

Air defense identification zones are declared by a number of countries to monitor and control aircraft approaching territorial airspace for national security purposes.

Russia and China do not recognize the South Korean air defense zone.