A South Korean fighter jet crashed southeast of Seoul on Thursday, leaving two pilots presumed dead, the air force said.
The jet was unrelated to US-South Korean military drills taking place in South Korea this month.
The annual joint military exercises were delayed by about a month for the Winter Olympics and to help create conditions for a resumption of talks between North and South Korea.
The F-15 jet was returning to base from conducting air manoeuvres when it crashed, an air force official said. He did not comment on the possible cause.