South Korea denied the accusations, but the North warned Sunday that the incident could escalate tensions.
“We urge the South side to immediately halt the intrusion across the military demarcation line in the West Sea that may lead to escalation of tensions,” the official Korean Central News Agency said. “It arouses our due vigilance as it may lead to another awful incident.”
South Korea’s military and coast guard responded to North Korea's claim of a border incursion by saying their ships and aircraft have been searching waters south of the boundary since Friday in case the official's body drifts back.
Officials in Seoul have said the 47-year-old was likely attempting to defect before North Korean troops aboard a boat fatally shot him and burned his body.
The message said North Korean troops shot the official because he attempted to flee after refusing to answer to questions. It said that North Korea maintained troops were unable to find the official's body and burned the object he was floating on in line with anti-coronavirus rules.
South Korean President Moon Jae-in's office said the country’s National Security Council viewed Kim's apology positively and proposed a joint investigation with North Korea to find out what happened to the official.
Kim is currently struggling to overcome worsening economic woes caused by U.S.-led sanctions over his nuclear program and the pandemic that forced his country to close its border with China, its biggest trading partner.
The Associated Press contributed to this report.