North Korean leader Kim Jong Un has issued a rare apology over the fatal shooting of a South Korean man to prevent the spread of COVID-19, South Korea's national security adviser disclosed, sparking public outrage in South Korea over the killing.

South Korean president Moon Jae-in was reportedly told by Kim that the killing should not have happened. The 47-year-old victim – who worked for the fisheries ministry – was found by soldiers floating in the North's waters. The man was then shot dead and his body set on fire, South Korean authorities said. However, Pyongyang insisted it had not set the man's body alight, but rather the "floatation device" that was carrying it, Reuters reported.

The shooting marks the first such death in around 10 years, occurring after North Korea taunted the South for months, blowing up a communications office in June this year north of the border. Built in 2018, the building served as a symbol of reconciliation between the two neighbors.

The rare conveyance of remorse from Kim came as South Korean President Moon Jae-in faced growing political backlash over the incident, which happened at the same time Moon pushed for renewed efforts for engagement with the North.

It has not yet been ascertained why the man was there and what he was doing. South Korean authorities said he may have attempted to defect to North Korea but his family said this is not true.

The border the separates South and North Korea is heavily secured, and Pyongyang is believed to have implemented a "shoot-to-kill" order to prevent the virus from infecting the country.

Based on the letter, which was sent by the United Front Department – a ruling Workers' Party that oversees relations between the two sides – Kim gave the order to send the message that he regrets what happened and is "very sorry the incident created a huge disappointment" to Moon and compatriots in the South, Bloomberg reported.

Moon lauded Kim's "strong resolve to save lives" and cited anti-pandemic and calamity recovery efforts in his Sept. 8 letter, his office disclosed.

North Korea said it hopes the shooting incident would not harm recent efforts by the two countries to promote trust, South Korean national security chief Suh Hoon said, adding the North and South Korean leaders have exchanged letters this month.

Meanwhile, experts say if there had not been an expression of regret, Kim's letter to Moon would have been for naught. By at least trying to ease the tension, the North Korean leader may be showing a willingness to keep communication lines open.