North Korean leader Kim Jong Un offered a rare apology Friday, South Korea said, after the killing of a South Korean civilian official near the countries' disputed sea border.

South Korea's military on Thursday accused North Korean forces of shooting and cremating the official, who Seoul believes may have been trying to defect to the North.

According to a statement announced by South Korea's presidential office, Kim is "greatly sorry" for disappointing South Koreans over the incident. The statement said the death was "unsavory" and "should not have happened."

The 47-year-old went missing Monday from his patrol boat about 10 kilometers south of the de facto inter-Korean border. Seoul officials suspect the man, who had reportedly struggled with debt and other personal issues, jumped overboard with a flotation device.

After being intercepted at sea by North Korean troops, the man was questioned, shot to death, doused with oil, and set on fire, apparently all on orders from a superior, according to the South Korean military's version of events.

North Korea gave a different account. It says the border troops, following anti-coronavirus guidelines, fired 10 gunshots at the man from a distance. When they approached his flotation device, they found only blood. They then set the floating device on fire, the statement said.

Rare apology

North Korea's apology was delivered to Seoul by the North's United Front Department, a ruling party body that handles inter-Korean ties. The letter expressed hope that "trust and relations" between the two Koreas will not be hurt.

It is extremely rare for North Korea to apologize. Following some past killings of South Korean civilians, the North expressed "regret," often later blaming Seoul for the incidents.

With Kim's apparent apology, the risk of escalation has been reduced, said Leif-Eric Easley, a professor at Ewha University in Seoul. He says the killing could have led to "tit-for-tat violations" of a military agreement meant to reduce tensions along the frontier.

"The shooting incident was also turning South Korean public opinion against offering peace and humanitarian assistance to Pyongyang. Kim's diplomatic move avoids a potential fight in the short-term and preserves the option of reaping longer-term benefits from Seoul," he added.

The shooting incident is awkwardly timed for South Korean President Moon Jae-in, who this week used a video speech at the United Nations General Assembly to call for an end-of-war declaration between North and South Korea. He also called for coronavirus-related cooperation.

The left-leaning Moon, who wants to improve ties with Pyongyang before he leaves office in 2022, has been trying to convince the North to return to the dialogue and cooperation that marked the beginning of his five-year term.

Moon-Kim letters

South Korea on Friday revealed that Kim recently exchanged letters with Moon, the first known recent dialogue between the two leaders.

In a letter dated September 12, Kim expressed sympathies for South Koreans battling the coronavirus, as well as recent typhoons.

"I sincerely wish for everyone's well-being," Kim said in the letter, which was released in full by the South Korean Blue House. Moon had sent Kim a message on September 8, according to Seoul.

Earlier this year, North Korea cut communications channels with the South and blew up the two countries' de facto embassy after complaining about South Korean activists who launched balloons filled with anti-Pyongyang propaganda across the border.

In June, Kim unexpectedly called off the pressure campaign. Since then, North Korea has been primarily focused on domestic issues, such as the coronavirus pandemic and devastating floods.

Coronavirus lockdown

North Korea has since issued "shoot-to-kill" orders to prevent the coronavirus from entering the country from China, the top U.S. commander in South Korea, General Robert Abrams, said earlier this month.

The coronavirus-related security zones were first reported by the Daily NK, a Seoul-based news website with sources in North Korea. The outlet said the new rules stipulated that anyone "breaking rules or disrupting public order near the border will be shot without warning." The rules apply to all areas of the country, it said.

"North Korea is locked down almost as in a wartime situation to prevent Covid-19 outbreaks," said Yang Moo-jin, a professor at the University of North Korean Studies in Seoul.

North Korea for months said it had no coronavirus infections, but eventually backed away from that assertion.

In July, a 24-year-old man who had fled North Korea swam back into the country, after being accused of rape in South Korea. That incident prompted the North to lock down a border area, ostensibly because of coronavirus concerns.