South Korea said Thursday North Korean troops fatally shot a South Korean government official who may have attempted to defect and set his body on fire, after they found him on a floating object in waters near the rivals’ disputed sea boundary.

According to Seoul’s announcement, the man disappeared from a government ship that was checking on potential unauthorized fishing in an area south of the boundary on Monday, a day before he was found in North Korean waters.

North Korea sent officials wearing gas masks aboard a boat near the man to learn why he was there on Tuesday afternoon. Later in the day, a North Korean navy boat came and opened fire at him, South Korea’s Defense Ministry said.

Sailors from the boat, putting on gas masks and protective suits, poured gasoline on his body and set it aflame, the Defense Ministry said, citing intelligence gathered by surveillance equipment and other assets.

It was also unclear how he ended up in the North. But a defense official said the man might have tried to defect to North Korea. The official, requesting anonymity citing department rules, said the official was wearing a life jacket on a small floating object and that the military had obtained information that he wanted to go to North Korea.

The official said North Korea may have determined to kill him in line with its stringent anti-coronavirus rules that involves shooting anyone illegally crossing the border.

North Korea has steadfastly said there hasn’t been a single virus case on its territory, a claim widely disputed by many foreign experts. Observers say a pandemic could cause devastating consequences in North Korea because of its broken public health care system and a chronic shortage of medical supplies.

South Korea sent a message to North Korea via a communication channel at the US-led UN Command in South Korea on Wednesday to ask about the missing official. But North Korea hasn’t responded, according to the South Korean Defense Ministry.

Senior military officer Ahn Young Ho told reporters Friday that South Korea strongly condemned North Korea’s “atrocious act” and urged it to punish those responsible. He said South Korea used various intelligence to hold North Korea responsible for the man’s death.

Little is known about the 47-year-old, except that he was among 18 officials aboard the government boat belonging to the Oceans and Fisheries Ministry. When his colleagues searched for him after his disappearance, they only found his shoes left on the ship. Days of search involving aircraft and vessels came up empty handed, according to the defense and oceans ministries.

The poorly marked western sea boundary is where several bloody naval skirmishes and two deadly attacks blamed on North Korea happened in recent years. The government ship was near South Korea’s Yeonpyeong Island, which was hit by North Korean artillery in 2010, killing four people.

The incident is expected to deepen already-strained ties between the rivals, whose exchange and cooperation programs have virtually all been suspended amid a deadlock in broader nuclear diplomacy between Pyongyang and Washington. In June, North Korea blew up an inter-Korean liaison office on its territory to protest South Korean civilians sending leaflets against the North across the border.

Conservative experts and politicians in South Korea argued that the government explanation the official might have attempted to defect lacked evidence. They say the government may want to prevent strong anti-North sentiments in South Korea to keep alive chances for talks with North Korea.

“A public servant defecting to North Korea? I think it sounds bit strange as he has a stable job security,” said Choi Kang, vice president of Seoul’s Asan Institute for Policy Studies. “Why did North Korea shoot a man defecting to the North voluntarily? I can also say the burning of his body was an attempt to conceal evidence.”

South Korea’s liberal government led by President Moon Jae-in has faced criticism by conservatives that it’s sympathizing with North Korea too much and fails to respond strongly enough to the North’s provocation, such as the liaison office destruction and crude insults.

In 2008, North Korean soldiers fatally shot a visiting South Korean tourist who wandered into a restricted area. South Korea’s then conservative government responded by suspending tours to the North’s scenic Diamond Mountain resort.

The main conservative People Power Party urged Moon’s government to take stern action. “The reason for the government’s existence is protecting its people and their property,” a party statement said.

Defections of South Koreans to North Korea are highly unusual. More than 30,000 North Koreans have fled to South Korea in the past 20 years for political and economic reasons.

In July, however, a North Korean defector slipped back to North Korea, prompting North Korea to impose a lockdown of a border city and declare a state of emergency over virus concerns.