Korea will expand its Air Defense Identification Zone in response to China's declaration of a new zone last week, a meeting chaired by chief presidential security advisor Kim Jang-soo decided Sunday.
The government will inform China, Japan and the U.S. of the decision rather than negotiating with them first.
Air defense identification zones, where overflying aircraft must identify themselves to the country that claims them, are subject to no international treaties. The zones of several countries in Asia overlap, and not every country has one.
Both the Chinese and Japanese zone include the submerged reef of Ieo Island, where waters are controlled by Korea, but Korea's does not.
Officials are minded to set the new boundaries flush with Korea Flight Information Region, which was created simply to ensure smooth air traffic flow and already includes a large part of Japan's identification zone south of Jeju Island as well as Ieo.
A government source said "multiple measures" have been drawn up, while "close scrutiny of relevant international laws has been completed."