Seoul - South Korea said on Sunday it has extended its air defence zone to partially overlap with a similar zone declared by China two weeks ago that has sharply raised regional tensions.
Beijing's unilateral declaration of an air defence identification zone in an area that includes islands at the heart of a territorial dispute with Japan has triggered protests from the United States and its close allies Japan and South Korea.
Announcing the expansion of its own zone to include two territorial islands to the south and a submerged rock also claimed by China, South Korea's Defence Ministry said the move would not infringe on neighbouring countries' sovereignty.
"We believe this will not significantly impact our relationships with China and with Japan as we try to work for peace and cooperation in Northeast Asia," defence ministry head of policy Jang Hyuk told a briefing.
"We have explained our position to related countries and overall they are in agreement that this move complies with international regulations and is not an excessive measure," he said, adding that the ministry's top priority was to work with neighbouring countries to prevent military confrontation.
South Korea objected to China's 23 November move as unacceptable because its new zone includes a maritime rock named Ieodo, which Seoul controls, with a research station platform built atop it. China also claims the submerged rock.
Still, South Korea's reaction to Beijing has been more measured than the sharp rebukes delivered from Tokyo and Washington, reflecting a sensitivity towards Seoul's largest trading partner.
South Korea's air defence zone was originally established by the US Air Force in 1951 during the Korean War. The extension of the zone will not apply any restrictions to the operation of commercial flights, the defence ministry said separately in a statement. The move will take effect on 15 December, it said.
It will also result in an overlap with Japan's air defence zone, Jang said.
There was no immediate reaction from China, although Beijing's response to news last week that South Korea was reviewing its options on the air defence zone was relatively low key.
Chinese Foreign Ministry spokesperson Hong Lei said on Friday that any move by South Korea must "accord with international law and norms", but added: "China is willing to maintain communications with South Korea on the basis of equality and mutual respect."
The decision by China that kicked off the latest spat was the subject of a tense disagreement as US Vice President Joe Biden visited China last week, stressing Washington's objections to the move that he said caused "significant apprehension" in the region.
In an implicit criticism of the way China expanded its air defence identification zone, the United States praised South Korea for its having consulted its neighbours - including China and Japan - before going ahead.
"We also appreciate the [Republic of Korea's] commitment to implement this adjustment to its [Air Defence Identification Zone] in a manner consistent with international practice and respect for the freedom of overflight and other internationally lawful uses of international airspace," State Department spokesperson Jen Psaki said in a statement.
"This approach avoids confusion for, or threats to, civilian airlines."
"The United States has been and will remain in close consultation with our allies and partners in the region to ensure their actions contribute to greater stability, predictability, and consistency with international practices," she added.
Ties between China and Japan, always fraught due to regional rivalry and lingering bitterness from World War Two, have been strained for months by the dispute over the islands in the East China Sea, called the Diaoyu by China and the Senkaku by Japan.
Washington takes no position on the sovereignty of the islands, but recognises Tokyo's administrative control and says a U.S.-Japan security pact applies to them.
Beijing says its zone is in accordance with international law and Washington and others should respect it.
Under the Chinese zone's rules, all aircraft have to report flight plans to Chinese authorities, maintain radio contact and reply promptly to identification inquiries.
U.S., Japanese and South Korean military aircraft have breached the zone without informing Beijing since it was announced. South Korean and Japanese commercial planes have also been advised by their governments not to follow the rules.