The government on Sunday announced a new air defense identification zone with the same boundaries as Korea's Flight Information Region and overlapping with both the Chinese and Japanese zones.
The new zone stretches 236 km south of the submerged reef of Ieo, which also lies in the Japanese and Chinese zones, and includes Marado and Hongdo, an inhabited island that is also part of Japan's zone.
The eastern and western boundaries remain the same as before.
The old zone had been in place since it was delineated by the U.S. Air Force in March 1951, in the middle of the Korean War, and was being seen as an anomaly here. The move comes after China unilaterally last month declared its own zone covering Korean-controlled airspace.
A high-ranking Defense Ministry official said, "The adjustment is in line with the international aviation order and international regulations. Ahead of the announcement, we offered sufficient explanations to related countries."
The official added that they understand "to a certain extent" that the changes are not "excessive."
The expanded zone will go into effect after a week's notice period on Dec. 15.
But Korea lacks the military capability to monitor and protect the widened zone. A military source on Sunday said in an emergency the Air Force's state-of-the-art F-15K fighter jets would be capable of engaging in maneuvers over Ieo for "only around 20 minutes," while the mainstay KF-16 fighter jets can only operate in the area for "three to five minutes" before having to return for refueling.
"Only the F-15Ks are capable of operating in the region," the source added.
They are stationed at an air base in Daegu, which is 520 km away from Ieo and makes operations there inefficient.
Defense Minister Kim Kwan-jin told lawmakers on Saturday that moving the F-15Ks to an air base in Gwangju "could shorten the time" required to mobilize the aircraft. The Gwangju base is around 90 km closer to Ieo.
But military officials said relocation is not being considered at the moment.