Former President Moon Jae-in on Thursday expressed deep concern over the prosecution's ongoing investigation into the 2020 death of a South Korean fisheries official at the hands of North Korea, saying that a "matter of national security" should not be a "subject of political strife."

"I express deep concern over making a matter of national security a subject of political strife and these senseless acts that incapacitate the national security system and stomp on the pride of public servants who have devoted themselves to protecting national security for a long time," Moon said in a statement read by Rep. Youn Kun-young of the main opposition Democratic Party.

Moon said his administration reached a conclusion that the official was killed while attempting to defect to the North, based on all the intelligence and circumstantial evidence it could get at the time.

It is the first time that Moon has publicly expressed his official stance on the probe since the incumbent government overturned in June the preceding Moon government's assessment that the official had tried to defect to the North.

Top security officials of the previous government, including former defense minister Suh Wook, have been questioned in connection with the case. On Tuesday prosecutors sought an arrest warrant for former National Security Adviser Suh Hoon over the case.

Moon called on the incumbent government to provide another explanation of how the official ended up in North Korean waters if it seeks to overturn the previous conclusion.

Moon also noted that the intelligence and the circumstantial evidence surrounding the slain official remain unchanged.

Lee Dae-jun, the 47-year-old fisheries official, was fatally shot by the North's coast guard near the Yellow Sea border between the two Koreas on Sept. 22, 2020, a day after going missing while on duty on board a fishery inspection vessel.

In June, the Coast Guard and the military reversed the Moon administration's conclusion, saying there was no evidence to suggest the deceased official had a motive to defect.

Since then, the prosecution has been looking into the possibility that the Moon government manipulated the case to curry favor with Pyongyang.

Youn, who served as a key presidential aide to Moon, also slammed the President Yoon Suk-yeol government and the prosecution over the investigation, calling it "political retaliation."