SEOUL, South Korea (AP) — South Korean troops were engaged in an operation near the heavily fortified border with North Korea on Wednesday after detecting “unidentified personnel” there, the South’s military said.

A Joint Chiefs of Staff statement said that South Korea’s surveillance equipment spotted a person on the eastern section of the Demilitarized Zone, a mine-strewn buffer zone that separates the two Koreas. It said it will disclose more details after the operation was finished.

South Korea’s Yonhap news agency, citing an unidentified military official, reported that searches were underway in the area after a person was believed to have climbed over a DMZ wire fence overnight. It said the person was believed to have tried to defect to South Korea. It wasn’t clear if the person is a soldier or a civilian.

More than 30,000 North Koreans have fled to South Korea in the past two decades, mostly via China, but a small number of North Koreans still occasionally escape through the DMZ land border. At the height of Cold War rivalry, both Koreas routinely sent agents and spies to each other's territory through the DMZ, but no such incident have been reported in recent years.

Yonhap said South Korea’s military boosted its anti-infiltration readiness level in the eastern front-line area on Wednesday, but the Defense Ministry said it couldn’t confirm the report.

The possible border breach came as South Korea’s government reopened the southern side of an inter-Korean border village to civilian visitors after halting tours for a year due to the spread of African swine fever in the region that forced workers to cull around a half a million pigs. That border village, called Panmunjom, is located on the western part of the land border.

Seoul’s Unification Ministry has said the tours to Panmunjom will begin on a trial basis on Wednesday before officially reopening on Friday.

The two Koreas remain split along the 248-kilometer (155-mile) long DMZ, the world’s most heavily guarded, since the end of the 1950-53 Korean War.

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Associated Press writer Kim Tong-hyung contributed to this report. .