SEOUL, South Korea — Searchers recovered the body of a South Korean pilot who was killed Thursday when his F-15K fighter jet crashed into a mountain in the country's rural south, the air force said. Workers planned to resume their search Friday for the co-pilot, who was also presumed dead.

It wasn't immediately clear what caused the crash or whether the pilots attempted to eject. The air force did not disclose their names or other details.

The air force said in a statement that the pilots were flying back to their base in the city of Daegu after an unspecified mission. It said no civilian injuries or property damage had been reported.

It took more than two hours for dozens of firefighters and rescuers to reach the wreckage on foot through heavy fog deep in the mountain, an official from the Chilgok Fire Department said.

An employee at a nearby golf club said he heard what seemed to be a series of explosions that also shook the club's building.

"The fog was very thick and we couldn't see anything clearly," said the employee at the Gasan Country Club, who said the crash site was in a mountain behind the club's fourth hole. "There were several bangs that went off between gaps of a few seconds."

The employee didn't want to be identified, saying he wasn't authorized to speak to reporters.