North Korea says it will take action against a South Korean fishing boat and its four-member crew in accordance with the results of the investigations.

The crew of the 29-ton “800 Yeonan-ho” is under investigation after the boat strayed into North Korean waters in the East Sea on Thursday.

North Korea informed the South of the investigation in a fax from a working-level military official based in the East Sea district on Friday afternoon. It is the first time for the North to send notification about the ongoing investigation.

An official from the Unification Ministry noted that the message did not state the name of the investigating body. He added that in the past, the North only sent messages to Seoul after completing investigations on seized personnel.

Concerns are mounting that Pyongyang may prolong the detainment of the fishermen as in the case of a South Korean worker held for four months at the Gaeseong Industrial Complex.