A South Korean official has been shot dead and burned by North Korean troops, said the South's defence ministry which condemned the "brutal act".
Seoul said the man had disappeared from a patrol boat near the border and was later found in the North's waters, reports BBC.
North Korean soldiers shot him, then poured oil over his body and set it alight, the ministry said. It had come to this conclusion based on its analysis of "diverse intelligence".
Pyongyang has not commented.
North Korea has tightened its borders and is thought to have a "shoot-to-kill" policy in place to prevent the coronavirus from entering the country.
'Found and executed'
South Korea's defence ministry said the official was working for the fisheries department and was on his patrol boat about 10km (6 miles) from the border with the North, near the island of Yeonpyeong, when he disappeared on Monday.
The 47-year-old father of two had left his shoes behind and appeared to have taken a life jacket. It is believed he had been trying to defect.
Seoul said a North Korean patrol boat later discovered the man in their waters, clutching a flotation device and exhausted.
He was questioned before a senior North Korean official allegedly ordered that the man be executed. North Korean troops wearing gas masks then burned the corpse, said South Korean defence ministry officials who added they believed this may have been an anti-coronavirus measure.
South Korea said it "strongly condemned such a brutal act and strongly urged the North to provide an explanation and punish those responsible."
The BBC's Seoul correspondent Laura Bicker says North Korean officials may be doing everything they can to ensure the country remains unaffected by the coronavirus pandemic. Authorities are thought to be preparing for a huge military parade on 10 October to mark the 75th anniversary of the foundation of the ruling Workers' Party.
Pyongyang closed its border with China in January to try to prevent contamination. In July, North Korean state media said the country had raised its state of emergency to the maximum level.
The commander of the US military's forces in South Korea, Robert Abrams, said in an interview last month that the North had introduced a new "buffer zone" of one to two kilometres on the Chinese border. He also said North Korea has special operation forces in place with orders to "shoot-to-kill" anyone coming across the border.
When briefing reporters on Thursday about the latest incident, South Korea's defence ministry officials said they had done a "thorough analysis of diverse intelligence".
But it was not clear how exactly they had gathered the information. The military hotline between North and South was cut in June, and the inter-Korean liaison office, which was built to help both sides communicate, was destroyed by North Korea.
Thursday's incident would be the second time North Korean troops have shot and killed a South Korean civilian. A tourist from the South was shot by a soldier at Mount Kumgang in July 2008.