SEOUL, South Korea — In a surprise move that could help ease tensions on the Korean Peninsula, North Korea said Thursday that it would release six South Koreans it has been holding in detention, South Korean officials said.

The Red Cross of North Korea told its South Korean counterpart that the six would be returned to the South on Friday at the border village of Panmunjom, the South Korean Unification Ministry said in a statement.

It was unclear who the detainees were. The ministry said that they were South Korean men between the ages of 27 and 67, but that it was unclear how long they had been in the North or how they had gotten there.

Pyongyang said in February 2010 that it was holding four South Koreans for illegal entry, but it never responded to Seoul’s request that they be identified and released. In June of this year, the North said it was holding “several” South Koreans for entering the country illegally, but it did not elaborate.