North Korea said Friday four South Koreans are under investigation for illegally entering the country.

Authorities "recently detained four South Koreans who illegally entered" North Korea, the North's official Korean Central News Agency said Friday. "They are now under investigation."

The brief dispatch did not identify the South Koreans or say when they allegedly enter the North.

The National Intelligence Service, Seoul's top spy agency, had no immediate comment on the report.

The announcement came weeks after North Korea freed Robert Park, an American missionary detained for illegally crossing its border on Christmas Day to call international attention to the country's alleged human rights abuses.

Last year, a South Korean pig farmer defected to North Korea by cutting through barbed wire at the heavily fortified border.

The two Koreas remain in a state of war because their three-year conflict ended in 1953 with a truce, not a peace treaty.