South Korea's air force says one of its F-15K fighter jets has crashed at a mountain in the country's rural south.

It isn't immediately clear what caused Thursday's crash or whether both pilots safely ejected.

The air force says crews are searching for the pilots.

An official from the Chilgok Fire Department says workers are approaching the site by foot and don't have visuals of the aircraft yet. He didn't want to be named, citing office rules.

An employee at a nearby country club says he heard what seemed to be a succession of explosions that also left the club's building shaking.