BEIJING, Dec. 9 -- China expressed regret over the decision of the Republic of Korea (ROK) to expand its air defense identification zone (KADIZ), a Foreign Ministry spokesman said on Monday.

Spokesman Hong Lei made the remarks after the ROK on Sunday announced a southward expansion of the KADIZ, encompassing submerged rocks within the overlapping exclusive economic zones (EEZ) of the ROK and China.

Hong said China and the ROK have maintained communication over the establishment of China's ADIZ and the expansion of the KADIZ.

The Chinese Foreign Ministry and the Defense Ministry have stated their position to the ROK side the first time and demanded the ROK side cautiously and properly handle the issues, he said.

"China is ready to maintain communication with the ROK side in line with the principle of equality and mutual respect," he said.

The ROK Defense Ministry said its eastern and western boundaries remained the same as before, and that the new zone would take effect from Dec. 15.

It marks the first change in more than six decades to the KADIZ, which was drawn in 1951 by the U.S. Air Force during the 1950-53 Korean War.

The ministry said the new zone included the nation's two southernmost islands of Marado and Hongdo, as well as the Suyan Rock, a submerged reef within the overlapping EEZ of China and the ROK.

Hong reiterated that an ADIZ is not part of a country's territorial airspace and has nothing to do with the administrative rights over sea and airspace. It is an international airspace demarcated outside the territorial airspace for the purpose of identification and early warning.

The Suyan Rock is an isolated underwater reef and is not a territory, thus territorial claims don't apply, he said, adding that it is a consensus between China and the ROK.

The Suyan Rock is located within the overlapping EEZ of China and the ROK, he said, noting that relevant issues can only be addressed through maritime boundary delimitation between the two countries in the East China Sea.