The F-15K Slam Eagle went down in the southern county of Chilgok, in North Gyeongsang province, on its way back to the Daegu Air Base after an hour-long mission.

"Bodies were found and we are checking their ID but both pilots are feared dead," the spokesman told AFP.

No ground damage was reported, he said.

The last crash involving a South Korean F-15K fighter was in 2006 when it fell into the Sea of Japan during a nighttime mission, killing both pilots.

Last year, an F-16D fighter crashed in North Gyeongsang but its two pilots ejected to safety.

South Korea's air force first introduced the F-15K, made by Boeing, in 2005. It operates more than 60 F-15Ks.