Two South Korean fighter jets crashed into a mountain Tuesday during a routine training mission, killing three airmen on board, the military said.

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Debris from crashed South Korean F-5 fighter jets lies in the snow on a mountain in Pyeongchang, South Korea, on Tuesday. ((Yoo Hyung-je, Yonhap/Associated Press))

The F-5 jets hit a mountain in Pyeongchang, about 180 kilometres east of Seoul, shortly after they took off from a nearby air base, an air force official said on condition of anonymity citing department policy.

Three airmen were aboard the jets, and rescuers later found body parts, uniforms and shoes at the crash site, the official said.

"We believe they all died on the job," he said.

The cause of the accident was not immediately known.

Yonhap news agency reported that at the time of the crash snow and strong winds were pounding the mountain, which was shrouded in heavy fog.

"There was a thundering noise and acrid smoke near the mountain's summit," Yonhap quoted witness Yoon Heung-joon as saying.

Yonhap said many climbers were on the mountain Tuesday, but the air force official said there were no immediate reports of casualties on the ground.