The JCS said it could not confirm whether the person was alive, but sent a notice to the North via a military hotline asking for protection.
The border crossing, which is illegal in South Korea, came as North Korea carries out strict anti-coronavirus measures since shutting borders in early 2020, though it has not confirmed any infections.
A public and political uproar emerged after North Korean troops shot dead a South Korean fisheries official who went missing at sea in September 2020, for which Pyongyang blamed anti-virus rules and apologised.
Two months earlier, North Korean leader Kim Jong Un declared a national emergency and sealed off a border town after a North Korean defector who he said had COVID-19 symptoms illegally crossed the border into the North from the South.
The North’s prolonged lockdowns and restrictions on inter-provincial movement have also pushed the number of North Korean defectors arriving in the South to an all-time low.
South Korea and a U.S.-led U.N. force are technically still at war with North Korea since the 1950-1953 Korean War ended in an armistice rather than a peace treaty.
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