South Korea’s air force said that two of its planes collided in midair and crashed on Friday, killing all four pilots on board.
The two KT-1 aircrafts crashed into a mountain in the southeastern city of Sacheon.
The air force added that it has formed a team to determine the cause of the accident and damage.
Over 30 firefighters and rescuers are conducting a search operation at the crash site, local media said.
Second South Korean air force crash this year
It comes nearly three months after a South Korean air force pilot died in January when his F-5E fighter jet crashed into a mountain in the city of Hwaseong.
The KT-1 is a single-engine basic trainer and light attack aircraft. It is built jointly by the state-run Agency for Defense Development and a contractor, Korea Aerospace Industries.