South Korea planned to announce an expanded air defense zone on Sunday, a move that could heighten tensions in the region where China has created a new air zone encroaching on its neighbors, dpa reported.
China's decision on November 23 angered South Korea and Japan, which refuse to recognize the unilateral move as legitimate.
South Korea has flown aircraft through it without providing prior identification. Seoul also decided to expand its own air zone after Beijing refused to back down during bilateral defense talks last week, Yonhap news agency reported.
"Ahead of the announcement, we will explain our position in detail to neighboring countries," a government official said on condition of anonymity.
"We will offer detailed explanations through defense and diplomacy channels so as not to hurt trust among the countries."
China said Seoul's new air zone "should be in line with international law and convention."
Beijing's move was regarded as a sign of taking its foreign policy assertiveness to a higher level, partly to counter Washington's efforts to increase US influence in Asia.
The issue was a key topic for US Vice President Joe Biden during his trip to Japan, China and South Korea. His talks with Chinese President Xi Jinping produced no breakthrough, however.