SEOUL, SOUTH KOREA – Defying both China and Japan, South Korea announced Sunday that it is expanding its air patrol zone for the first time in 62 years to include a parcel of airspace over the East China Sea that is also claimed by ­Beijing and Tokyo.

South Korea's expanded "air defense identification zone" is the latest sign of a broadening discord among the Northeast Asian neighbors, who are already locked in territorial and historical disputes.

With South Korea's newly expanded zone, the air defense zones of all three countries now overlap over a submerged reef called Ieodo in South Korea and Suyan Rock in China. The reef is controlled by South Korea, which maintains a maritime research station there, but China also claims it. The seabed around the reef is believed to be rich in natural gas and mineral deposits.

The South Korean move came two weeks after China stoked regional tensions by unilaterally expanding its own air patrol zone to partly overlap with South Korea's and include airspace over the reef. The expanded Chinese air control zone also covers a set of East China Sea islands, called Diaoyu in Chinese and ­Senkaku in Japanese, which are at the heart of a territorial feud between Japan and China.

Airspace was a major topic when Vice President Joe Biden visited Japan, China and South Korea last week.

No effect on civilian flights

With its announcement on Sunday, South Korea expanded its air defense zone more than 186 miles to the south. It said its new zone would take effect in a week. There was no immediate response from Beijing or Tokyo.

The expanded air defense zone follows the boundaries of South Korea's existing "flight information region," an area assigned to South Korea for civilian air traffic control under an agreement with the International Civil Aviation Organization. It will have no effect on civilian flights, said Kim Min-seok, a spokesman for the South Korean Defense Ministry.

But the announcement of the expanded zone raises the risk of an accidental military clash in the region. A military plane entering another country's air defense identification zone must notify that country in advance. If it does not do so, the country operating the zone may order it to leave, or ­dispatch military jets to confront the intruding aircraft.

Maj. Gen. Chang Hyok, a senior policy coordinator at the South Korean Defense Ministry, said Sunday that his government had explained its air patrol zone to China and Japan. President Park ­Geun-hye also discussed it with Biden on ­Friday.

"Our top priority is to prevent accidental military clashes in the area," Chang said at a news briefing.

The State Department offered support for South Korea's approach, saying that keeping open the lines of communication with China and Japan "avoids confusion for, or threats to, civilian airlines."

The United States "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," said Jen Psaki, a State Department spokeswoman.