North Korean leader Kim Jong-un (left) and South Korean president Moon Jae-in (right). (File photo)

SEOUL – South Korea will demand that North Korea carry out another investigation into its recent killing of a Seoul fisheries official near the tense sea border, as the North's explanation bore some key discrepancies from Seoul's account, the presidential office said Saturday. 

On Tuesday, North Korean troops shot the 47-year-old man who was adrift in its waters and incinerated his body, according to the South Korean military.

He went missing the previous day while on duty near the Yellow Sea border island of Yeonpyeong.

North Korean leader Kim Jong-un apologized for the incident Friday in a message sent by the United Front Department, a key espionage agency handling inter-Korean affairs.

Pyongyang claimed that what it set on fire was not his body but an object he was using to stay afloat.

After holding the National Security Council (NSC) session late Friday, the Seoul government decided to demand further investigation and request a joint probe, if necessary, the presidential office said.

"As there exist differences between North Korea's explanation and our intelligence analysis, we decided to continue our investigation into the incident to reveal the truth," it added.

It also vowed to "swiftly take steps to further heighten a surveillance posture in the Yellow Sea to prevent such an incident from happening again."

Another issue in question is whether the official had an intention to defect to the communist country.

Military officials here said the man was presumed to have jumped into the sea on Monday in a suspected attempt to defect to the North, but the message from North Korea only noted that "the illegal intruder was to flee" while disobeying its verbal security checks.

Another issue in question is who ordered the killing.

South Korean officials said the brutal act appears to have been done in accordance with "orders from a superior authority," though they said they could not confirm exactly who approved the killing.

The North, however, said the decision was made by the chief of the patrol boat and that the actions taken were in line with its code of conduct. (Yonhap)