SEOUL, Oct. 4 (Yonhap) -- A Japanese destroyer briefly violated South Korea's air defense zone near the easternmost islets of Dokdo last month, but turned back to its planned route after a warning from the South's military, a military source said Thursday.

The Japanese destroyer, believed to be a 4,200-ton warship, came as close as 30 miles (48 kilometers) to the South's Korea Air Defense Identification Zone (KADIZ) near Dokdo on Sept. 21, the source said on the condition of anonymity. Foreign airplanes and ships are required to get approval from South Korea's military before entering the KADIZ.