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South Korea on Sunday announced the expansion of its air defense identification zone, extending it farther south into an area that overlaps with similar zones maintained by Japan and China.

The South’s decision, widely expected after a week of government discussions, marks the latest move in a regional struggle over airspace above the East China Sea.

South Korea’s Ministry of ­National Defense said the new zone would include two small islands and a submerged rock that is the subject of a long- running dispute with China. Air defense identification zones are not territorial claims, but they mark airspace that countries consider important to monitor. Officials in Washington and across Asia say the competing aerial zones raise the risk of mishaps that could trigger a broader conflict.

South Korea plans to hold talks with “related countries” to “prevent accidental military clashes” within the expanded zone, the Defense Ministry said in a statement. The South said the zone, known as an ADIZ, would take effect this coming Sunday.

The U.S. State Department, in a statement released after the South Korean announcement, said it had “conferred” with Seoul on the expansion, including in a meeting Friday between South Korean President Park ­Geun-hye and Vice President Biden.

“We also appreciate [South Korea’s] commitment to implement this adjustment to its ADIZ in a manner consistent with international practice and respect for the freedom of overflight and other internationally lawful uses of international airspace,” the statement said.

There was no response from China on the move, but a Chinese Foreign Ministry spokesman said Friday that the South’s expansion “should comply with international laws and conventions” and that Beijing is “ready to stay in communication” with Seoul.

China two weeks ago declared its own ADIZ across a wide section of the East China Sea — a move that Seoul, Tokyo and Washington have protested. China’s new aerial zone includes a rock 15 feet below the water’s surface known internationally as Socotra. The formation lies within the economic zones of both China and South Korea, and it has long been a point of modest contention between the neighbors.

The rock is controlled by South Korea, where it is known as Ieodo. Seoul uses the site as an oceanic research center, having constructed an orange tower of beams and a helipad atop the rock in 2003. The research center has solar panels, wind monitors, barometric sensors and a solar radiation measurement system, and the monitoring data are displayed in real time on a government Web site.

Before the expansion, South Korea’s ADIZ did not include the submerged rock. For that reason, many lawmakers here said the zone was in need of an update. The South Korean ADIZ was drawn up in 1951 by the U.S. Air Force during the Korean War and overlaps with the southern part of North Korea.