SEOUL — A South Korean fisheries official who went missing from a patrol boat this week was found in the sea by North Korean troops and executed, in what appeared to be an ill-fated attempt to defect, Seoul's Defense Ministry said Thursday.

The North Korean troops, wearing gas masks, then doused the man's body in oil and set it on fire, seemingly to prevent the possible spread of the novel coronavirus, the ministry said in a statement.

The 47-year-old disappeared from the ship on Monday just south of the two countries’ disputed maritime boundary. Dressed in a life jacket and clutching a floating object, he was found a day later by North Korean personnel.

More than 33,000 North Koreans have fled to the South since the early 1990s to escape poverty and political oppression. But it is extremely rare for South Korean nationals to attempt to defect to the North.

Citing intelligence sources, the military said the man appeared to have been questioned at sea, north of the disputed boundary and about 24 miles from where he went missing, before he was executed on an “order from a superior authority.”

“Our military strongly condemns such an atrocity, and strongly demands North Korea provide explanations and punish those who are responsible,” Gen. Ahn Young-ho, who is in charge of operations at South Korea’s Joint Chiefs of Staff, told a news conference.

The incident dealt a blow to South Korean President Moon Jae-in’s efforts to improve relations with the North.

In a speech to the United Nations on Tuesday, Moon called for a formal end to the Korean War, arguing that would pave the way to denuclearization and a permanent peace on the peninsula. The 1950-53 conflict ended with an armistice, not a peace treaty.

South Korea said it sent a message to the North on Wednesday about the defecting official’s fate but had not received a response. There was no immediate comment on the incident in North Korea’s state media.

Suh Choo-suk, first deputy chief of South Korea’s National Security Council, called on North Korea to “take full responsibility and clarify the truth.”

Colleagues found only the man’s shoes on the vessel and reported his disappearance to the Coast Guard, prompting a search operation involving about 20 boats and aircraft, the Yonhap news agency reported.

Gen. Robert Abrams, the commander of U.S. Forces Korea, said earlier this month that North Korean troops manning the border with China had been given “shoot-to-kill orders” to prevent anyone from bringing the coronavirus into the country.

A North Korean defector who settled in the South was arrested by the South Korean police last week for breaking into a military training site near the border. The police said he was attempting to head back to the North.

Another defector who had crossed the border into the South three years ago swam back across the maritime frontier to North Korea in July. Pyongyang claimed he was a possible coronavirus carrier and locked down a border city where he had been present.

Denyer reported from Tokyo.