The Democratic People's Republic of Korea's (DPRK) leader Kim Jong Un expressed regrets over the death of a missing official of the Republic of Korea (ROK), the ROK national security adviser, Suh Hoon said on Friday.

DPRK leader Kim Jong Un sent a letter to ROK President Moon Jae-in, saying he feels "very sorry" and the incident should not have happened, the official told a briefing.

Kim said he wishes the confidence between the two nations is not damaged, the official said.

The rare conciliatory message from the DPRK leader came as Moon faced intense political fallout over the incident, which coincided with a renewed push by him for engagement with DPRK.

"Chairman Kim Jong Un asked to convey his feeling that he is greatly sorry that an unexpected unsavoury incident occurred in our waters which hugely disappointed President Moon Jae-in and compatriots in the South," the adviser, Suh Hoon, told reporters.

The DPRK told the ROK its troops operating near the western sea border fired more than 10 shots against the ROK man intruding into the DPRK's waters as part of "infection control measure."

The DPRK added that it had burned the floating device that the ROK man was on, not his body, Suh said.

DPRK expressed hope the incident would not undermine recent efforts to foster trust, Suh said, adding Moon and Kim had exchanged letters this month.

Moon praised Kim's "strong resolve to save lives" and steer anti-virus and flood recovery work in his September 8 letter, his office said.

In a September 12 reply, Kim said Moon would win the battle against the coronavirus and "good things" would happen later.

The leaders have held three summits and signed pacts to ease tension since 2018, but relations have soured since the collapse last year of a second summit between Kim and U.S. President Donald Trump, at which Moon had offered to mediate.

(With input from Reuters)

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