South Korea is seeking to buy two more early warning planes to step up its aerial surveillance capabilities over its expanded air defense identification zone, the Air Force said Wednesday.

The South Korean Air Force has operated four Boeing 737-based Peace Eye airborne early warning and control aircraft since 2011.

The number is dwarfed by Japan's 13 early warning planes.

In December last year, South Korea announced a new Korean air defense identification zone (KADIZ) to counter China's unilateral declaration of its own. The move aimed to bolster Seoul's sovereignty over a reef and other islands off the southern coast of the Korean Peninsula.

"For surveillance over the KADIZ, we are seeking to secure two more such planes over the long term," said an official at the Air Force, asking not to be named.

Peace Eye is able to detect and watch about 1,000 flying objects at the same time at 360 degrees. It is capable of detecting all low-altitude planes infiltrating through mountainous regions. (Yonhap)