The South Korean government said it plans to announce an expanded air defense zone on Sunday, amid a growing regional row following China's unilateral expansion of its own.   

The Ministry of National Defense will declare the expanded air zone early Sunday at its headquarters, with the exact time of the release to be announced soon, ministry officials said.  

Tension has been running high in East Asia since China unexpectedly announced on Nov. 23 an air defense identification zone above the East China Sea, which overlaps those of South Korea and Japan, and includes the South Korean-controlled reef of Ieodo and some small islands.  

It is widely expected that the government will not only specify Ieodo in the expansion outline, but the two southernmost islands of Marado and Hongdo as well.   

Seoul was going to announce the expanded air zone earlier but decided to put it off until it held talks with Washington, Beijing and Tokyo.    

China's proclamation of the bigger air zone is seen as a sign that the country is taking its foreign policy assertiveness to a higher level, partly to counter U.S. efforts to increase its political clout in the region under President Barack Obama's "pivot to Asia" policy.   

When South Korean President Park Geun-hye met with U.S. Vice President Joe Biden in Seoul on Friday, the air zone row was one of the key topics in their talks.   

Park apparently explained South Korea's position on the issue to Biden, asking for U.S. backing, to which he responded vaguely and caused confusion among South Koreans.   

But later the U.S. State Department said that the U.S. "is on the same page" with South Korea, in what was interpreted by local media here as an act of reassurance.