A South Korean official who went missing this week was questioned by North Korean troops, shot dead, and cremated, according to the South's military.
They said Thursday that the man had disappeared from a fisheries patrol boat and that evidence suggests he was trying to defect -- to the North.
The man had been reported missing Monday just 10 kilometers south of the Northern Limit Line, a disputed border on the water between the North and South.
General Ahn Young-ho from South Korea's Joint Chiefs of Staff spoke on Thursday.
"Our military strongly condemns such an atrocity, and strongly demands North Korea provide an explanation and punish those who are responsible."
They said the exact reason the 47-year-old official was shot is still unknown.
North Korean troops may have been acting under anti-coronavirus orders.
Citing intelligence sources, the military said the unidentified man appeared to have been questioned on a North Korean boat before he was executed on an "order from a superior authority."
They also said troops in gas masks then doused the body in oil and set it on fire.
North Korea says it has no cases of COVID-19.