South Korea said it plans to expand its air-defense identification zone to cover an area of ocean contested with China, a response to Beijing's recent move to create
an air-defense zone in the East China Sea.
The South Korean zone will incorporate airspace above a submerged rock claimed by both Beijing and Seoul that falls within China's zone. The move was widely expected and will take effect Dec. 15.
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Beijing's establishment late last month of a new air-defense zone angered the U.S. and Japan, which see it as a step to assert China's control of the East China Sea area and bolster its claim to islands administered by Tokyo.
Seoul also raised objections because the new Chinese zone overlaps with South Korea's air-defense zone and covers a submerged reef called Socotra Rock. South Korea and China have for years contested the rock, known as Ieodo in South Korea and Suyan in China, and economic rights to the ocean area around it.
South Korea built a nautical research station on the rock in 2003, giving it effective control. It lies southwest of the Korean peninsula, about 105 miles from the nearest South Korean land territory and 180 miles from the closest Chinese land.
In November, Seoul called on Beijing to redraw its air-defense zone to reflect its concerns. After the demand was rejected, South Korea said it would consider expanding its own zone.
The move to proceed is unlikely to significantly raise tensions in the region. China has reacted calmly to the South Korean plans, which have also been accepted by the U.S. and Japan.
In Beijing on Friday, a Chinese foreign ministry spokesman said South Korea should observe international law in expanding its air-defense zone, but said it didn't affect maritime claims because the zones are designed only to identify aircraft outside territorial airspace.
"South Korea should be in line with international laws and conventions. China will stay in communication with South Korea," said the spokesman, Hong Lei.
Vice President Joe Biden and South Korean President Park Geun-hye discussed South Korea's plans to extend its air-defense zone in a meeting in Seoul on Friday. A senior U.S. official said that Mr. Biden "expressed understanding" for South Korea's approach. The expansion also overlaps with Japan's air-defense zone but doesn't cover any Japanese territory. A spokeswoman for Japanese Prime Minister Shinzo Abe said the Korean move didn't pose a problem for Tokyo because Seoul made clear the zone wouldn't infringe on the freedom of travel by commercial planes.
"Unlike the Chinese action, we reached an understanding beforehand, so this would not create an immediate problem for Japan-Korea relations," Hikariko Ono said.
South Korea's defense ministry played down the possibility of airborne clashes or accidents because of the extended South Korean zone.
"We will coordinate with related countries to fend off accidental military confrontations and to ensure safety of airplanes," Defense Ministry spokesman Kim Min-seok said.
Analysts said that South Korea has been seeking to extend its air-defense zone to cover Socotra Rock for years and China's latest move gave it a reason to do so.
"It was a good time for Korea to claim what it wanted, although there's no real impact on the territorial issue over Ieodo," said Yang Uk, a senior research fellow at the Korean Defense and Security Forum, a think tank in Seoul.
South Korea's air-defense zone was drawn up by U.S. military forces in 1951 during the Korean War and covers airspace over North Korea.
An American defense official said the U.S. was "generally supportive" of the South Korean air defense zone. U.S. defense officials noted the new South Korean ADIZ had not been established over an area as hotly contested as the islands in the East China Sea where Beijing declared its zone last month.
Although American officials acknowledged Seoul's new zone encompasses disputed area, they maintain it will not change the "status quo" in Asia as they believe China has attempted to do.
Most importantly, U.S. officials said that, unlike Beijing, the South Koreans followed international norms and standards in establishing their zone and consulted widely before announcing it.
South Korean officials discussed the zone with Chinese, American and Japanese officials before moving to make it official. American Defense officials, anxious to encourage cooperation between Tokyo and Seoul, were particularly pleased that South Korea consulted extensively with Japan on the new zone.
The State Department said the South Korean zone spares civilian aircraft from confusion and threats.
—Jeremy Page and George Nishiyama contributed to this article.
