China expressed "regret" over South Korea's expansion of its own air defense zone that overlaps a larger part of those of China and Japan. South Korea on Sunday announced an expanded air defense identification zone (ADIZ) over the East China Sea to counter China's unilateral declaration of its own, RT reported. The move bolsters Seoul's sovereignty over a reef and other islands off the Southern coast of the Korean Peninsula, Yonhap said. China expresses regret over Seoul’s decision of expanding the ADIZ, foreign ministry spokesman Hong Lei said Monday.