A Japanese naval destroyer violated Korea's air defense identification zone near the easternmost islets of Dokdo on Sept. 21, the military said Thursday.

"A Japanese vessel believed to be a 4,200-ton destroyer approached within 48 km east of Dokdo on Sep. 21," a military source said. An SH-60 helicopter conducted two takeoff and landing drills aboard the destroyer.

/Newsis

The Korean military deployed an F-15K fighter jet, Lynx helicopter and destroyer. The Japanese destroyer turned back after being warned and sent a radio message saying it was en route to Vladivostok for training and intended no harm, the source added.

The air defense identification zone separates the country's air space into three zones over the East, West and South Sea and encompasses areas that are larger than those covered its sovereign air and maritime boundaries. Any foreign vessel or aircraft must obtain permission before entering.