North Korea repatriated six South Korean citizens at a heavily defended border crossing on Friday, South Korea's Ministry of Unification said, in a rare humanitarian gesture amid persistent tensions between Pyongyang and Seoul.
The six crossed from North to South over the low concrete step that divides the two Koreas at Panmunjom, a jointly-controlled "truce village" which straddles both sides of the Korean Demilitarized Zone and hosted the signing of the armistice that ended the 1950-53 Korean War.
North Korean state media said the group entered North Korea illegally and was released on humanitarian grounds after the six "honestly admitted to and repented on their crimes".
"They were investigated by the relevant institutions which generously pardoned them and allowed them to return to the South, where their families are," a statement carried by North Korea's KCNA news agency said.
Tensions between North and South Korea soared earlier this year as Pyongyang reacted angrily to tightened U.N. sanctions imposed in response to its latest nuclear test, but then eased for several months.
The North's statements have become increasingly bellicose towards the South's government and its president, Park Geun-hye, a change of tone reminiscent of the aggressive rhetoric it used towards her predecessor, Lee Myung-bak.
North Korean state media referred to Park by name for the first time this month and she has since become the subject of articles published nearly daily by the isolated country.
Speaking before the handover of the six South Koreans, who were immediately taken away for questioning, government officials in Seoul said their identity was unclear. They said an investigation would be conducted to determine how they were able to enter North Korea.
The returnees, aged 27 to 67, have only been identified by their family names. A Ministry of Unification spokesman said four of them might be a group of South Korean citizens that Pyongyang said illegally entered North Korea in 2010
Unauthorized visits to North Korea by South Korean citizens are illegal under South Korea's anti-communist National Security Law which prohibits interaction with North Korean nationals or possession of North Korean publications.
Last year, a pro-North Korean unification activist was arrested by South Korean authorities for a three-month unauthorized visit to Pyongyang.
Access to North Korean websites is blocked from South Korea and jamming towers prevent signals from Pyongyang radio stations reaching Seoul.
In 2010, a South Korean baby photographer received a 10-month suspended prison sentence for satirically retweeting propaganda from North Korea's official Twitter account.