Seoul , South Korea ( CNN ) -- South Korea on Monday reprimanded five senior military officials after admitting that a North Korean soldier had managed to cross the heavily patrolled border between the two countries undetected and knock on the door of his enemy 's barracks . Revelations about the ease with which the North Korean soldier reached the South Korean side of the border , considered to be the most heavily militarized in the world , have prompted criticism of the nation 's military . Read more : S. Korea fires warning shots at N. Korean fishing boats . The soldier , whose name and rank were not disclosed , jumped three barbed-wire fences along the eastern part of the border without being spotted on October 2 , according to the South Korean Defense Ministry . He was picked up by South Korean soldiers in the province of Kangwon only after he knocked on a barracks door , wishing to defect , the ministry said . He had escaped from his unit and traveled about 50 kilometers ( 31 miles ) through North Korean territory to get to the border zone . South Korean Defense Minister Kim Kwan-jin made a public apology in a live broadcast on national television Monday , calling the incident `` a clear failure in security operations . '' `` As the defense minister , I express sincere apology for causing concern to our people , '' he said . Read more : N. Korea taunts S. Korean candidate with 'Gangnam Style'-inspired video . Kim said a lieutenant general , two major generals and two brigadier generals were facing disciplinary action . He also pledged to enhance security measures and increase the number of soldiers around the border area . The security breach was deemed `` lamentable '' in an editorial last week by The Korea Times , an English-language newspaper . `` What if the defector were an agent armed with guns and grenades who sneaked into the barracks on orders from the North ? '' the editorial asked . It also criticized the initially misleading information about the situation from defense officials . The South Korean military had announced a subsequent defection across the border on October 6 , in which a North Korean solider on guard duty at the border told authorities in the South that he had killed his superiors before fleeing across the Military Demarcation Line . North Korean soldier shoots comrades before defecting to South . At the time , defense officials said it was the first defection over land since March 2010 . But news of the controversial October 2 defection and another in September later emerged after a South Korean lawmaker , Kim Kwang-jin from the main opposition Democratic United Party , questioned officials from the Joint Chiefs of Staff in a parliamentary hearing last week . In a statement , he criticized the `` lies and deception from the military . '' According to the lawmaker , at least 10 divisions from the South Korean army and two Marine Corps divisions are guarding the roughly 250-kilometer-long border area . Defections over land through the heavily armed and patrolled border area are rare , as most prefer to try crossing by sea or going through China . More than 24,000 refugees have entered the South from the North since the country 's division , according to the Ministry of Unification in Seoul .
The North Korea - South Korea border is considered the most heavily militarized in the world . This time , a North Korean soldier crossed it undetected . He is one of three killed in the past six months , a lawmaker says . The South Korean defense minister apologizes for the military failure .