SEOUL, South Korea (AP) — South Korean authorities on Thursday were questioning a suspected North Korean resident who crossed into the South, according to South Korea’s military.

South Korea’s Joint Chiefs of Staff said in a text message to reporters that South Korean soldiers secured an unidentified individual who was likely North Korean and handed that person over to relevant authorities for questioning.

The joint chiefs didn’t immediately provide details on how the person crossed the border, from where and whether it was an attempt to defect to the South, citing the ongoing investigation.

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The military statement came after South Korea’s Yonhap news agency, citing anonymous military sources, reported that a North Korean resident crossed an estuary where the Han River meets the Yellow Sea and was taken by South Korean troops at the South’s western border island of Gyodong.

South Korean Defense Minister Shin Won-sik, when asked about the report during a parliamentary session, said South Korea’s National Intelligence Service was investigating related matters but didn’t provide more details. The spy agency said it couldn’t immediately provide further information beyond what the military announced.

Tensions between the war-divided rivals are at their highest in years as North Korean leader Kim Jong Un continues to use Russia’s war on Ukraine as a distraction to further accelerate his weapons development and continues verbal threats of nuclear conflict with Washington and Seoul.

In response, South Korea, the United States and Japan have been expanding their combined military exercises and sharpening their nuclear deterrence strategies built around strategic U.S. military assets.

The joint chiefs said it wasn’t detecting any unusual military activity from the North as of Thursday evening.