North Korea returned six South Koreans across the border at 5 p.m. on Friday at the truce village of Panmunjeom.
 
Seoul's Unification Ministry said it will question the six men on how and when they entered the North and if they entered voluntarily.
 
The oldest of the group is 67 years old and has been identified by his surname Yun. The youngest is 27 and has the surname Song.
 
The ministry said the men could be prosecuted for violating the National Security Law if it’s discovered they voluntarily entered North Korea without government approval.
 
Among the group, four are likely to be people North Korea said it was investigating for illegal entry in February 2010.
 
A ministry official said this is the first time North Korea has returned South Koreans without any preconditions.