China on Monday expressed regret over South Korea’s declaration of an expanded air defense identification zone, which overlaps with those of China and Japan.

Seoul’s decision was announced Sunday amid high tensions sparked by Beijing’s unilateral declaration of a new air zone in the East China Sea, which incorporates Ieodo, a submerged rock controlled by South Korea, and a chain of disputed islands claimed by both Japan and China.

“The ROK (Republic of Korea) notified China of its expansion of the zone,” China’s Foreign Ministry spokesperson Hong Lei told reporters during a regular briefing. “China expresses its regret over the ROK’s decision to expand its ADIZ.”

Tokyo, which has strongly protested Beijing’s expanded air zone, did not take issue with Seoul’s decision.

“We don‘t think it’s going to be a problem at the moment,” Japan’s Chief Cabinet Secretary Yoshihide Suga told reporters. “It is different from the one announced by China because it does not cover our country’s territorial air, water or land,” he added.

As a follow-up to Sunday’s declaration of an expanded air defense identification zone, South Korea is stepping up its aerial patrol activities. The expansion is to go into force on Sunday.

The Navy flies its P3-C maritime patrol aircraft every day in the airspace over the submerged rock of Ieodo in the East China Sea, which Beijing has unilaterally incorporated into its new air defense zone. Previously, it patrolled the area two to three times a week.

The Air Force also plans to strengthen its monitoring activities in the air defense zone. The country’s maritime police are expected to increase patrol activities with their own fleet of aircraft.

President Park Geun-hye said Seoul’s decision to expand the air zone was a “prudent” one to maximize national interests.

“Recently, security conditions have been changing rapidly in areas surrounding the Korean Peninsula. A series of issues including the air defense zone and a change in the North Korean leadership have raised tension in the region,” she said during a meeting of senior presidential secretaries.

“Every single issue is a crucial one that could influence the future of our nation, and the government is trying its best to stably and prudently manage the situation under the consistent principles prioritizing national interest and trust building.”

Seoul’s expanded zone includes Ieodo in the overlapping exclusive economic zones of South Korea and China, and Hongdo, an uninhabited island south of Geojedo Island. Set up in 1951 by the U.S. military during the Korean War, the previous zone did not cover some of the country’s remote islands.

With the expansion of Seoul’s zone, Ieodo now falls into the air defense zones of three countries including Japan. Seoul plans to hold consultations with Tokyo and Beijing over how to handle the overlap of their zones on a bilateral or multilateral basis.

Cheong Wa Dae, the Prime Minister’s Office and other related government agencies will hold a policy consultative meeting on Tuesday to discuss administrative procedures to implement the expanded air zone and coordination with neighboring states.

When the expansion goes into effect on Sunday, foreign aircraft must file with the Seoul authorities their flight information 15 to 30 minutes before entering South Korea’s air defense zone. If they do not give notice, Seoul’s fighter jets could be deployed to fend off entry of unidentified aircraft for the purpose of national security.

Following China’s unilateral demarcation of the air defense zone last month, tension in Northeast Asia has sharply risen. China’s move was perceived by the U.S., Japan and other countries as an attempt to alter the status quo in the region in favor of its own national interest.

By Song Sang-ho (sshluck@heraldcorp.com)