A South Korean Navy patrol plane with four people on board crashed on a mountain in Pohang, a city in the south-eastern part of the country.
The Yonhap news agency reported on Thursday, citing authorities.
The crash happened at 1:50 pm (0450 GMT).
According to the report, witnesses said smoke was seen rising from the mountain.
The bodies of all four people aboard the plane have since been recovered, Yonhap reported.
The navy, in a short statement to reporters, said the crash occurred after the aircraft took off for a training exercise, but crashed due to unidentified reasons.
The navy said that it is investigating further details.
Fire workers were dispatched to the scene to extinguish the blaze.