Defense Minister Kim Kwan-jin publicly apologized Monday for the undetected defection early this month of a North Korean soldier across the heavily armed inter-Korean border. He pledged to sternly punish military officers responsible for the incident and thoroughly investigate flaws in the front-line guard system.

All necessary measures should be taken to prevent such grave border security failure from being repeated in the future. It cannot be excused for any reason that no one detected the North Korean soldier until he knocked on the door of front-line South Korean barracks to say he was defecting.

Another minister may have to apologize for a separate case that shows the lax discipline in the civil service.

A day before the defense chief offered the apology, a 61-year-old man set fire to a government complex building in central Seoul before killing himself. The former bank employee, who had long received treatment for depression, used the gasoline he was carrying to start the fire at an Education Ministry office on the complex’s 18th floor and then jumped to his death.

He was found to have passed the security line with a fake government ID to enter the government building, which houses the Unification Ministry, the Public Administration and Security Ministry and several other agencies.

The incidents in the front line and the government complex have raised serious concerns over the discipline and security posture in the military and officialdom. Sunday’s arson case might have further angered President Lee Myung-bak, who summoned the defense minister last week to rebuke the military for the border guard failure and order stern punishment against those responsible for it.

Applying the same standards, Lee will have to scold the public administration and security minister, whose office is in charge of protecting government facilities, for the loose checking system.

What the undetected defection on Oct. 2 concerned the public most was that the front-line unit would have suffered grave casualties if armed North Korean troops had infiltrated like that with the intent to attack. The same question can and should be raised about Sunday’s incident.

It worries us to think it possible for a North Korean agent to enter a key government building so easily at a time when Pyongyang has threatened to attack South Korean media and other organizations hostile toward it.

The security posture both along the front line and at the rear should not be eased but strengthened during periods of power transition. One of Lee’s final tasks as president is to tighten the discipline in the military and civil service to toughen up their security posture until he leaves office in February.