North Korea's announcement today came hours before US Secretary of Defence Jim Mattis visited the heavily-armed land border between the Koreas and stressed Washington's commitment to defend ally Seoul against North Korean threats.
Experts say it's unclear whether the North's gesture reflects intentions to improve relations with the South amid heightened animosity over Pyongyang's expanding nuclear programme.
Seoul's Unification Ministry says North Korea last detained a South Korean fishing boat in 2010 before repatriating it.