North Korean defence minister Hyon Yong-Chol has been executed by anti-aircraft fire for disloyalty and showing disrespect to leader Kim Jong-un, South Korea's intelligence agency says.

Hundreds of officials watched Hyon's execution at a military academy in northern Pyongyang on April 30, Han Ki-Beom, the deputy director of the South's National Intelligence Agency, told a parliamentary committee.

Executed: Hyon Yong-Chol, North Korea's Minister of the People's Armed Forces, at a conference in Moscow last month. Credit:Reuters

Hyon, who was appointed to the post of Minister of the People's Armed Forces less than a year ago, was apparently caught dozing off during formal military events and also talked back to Kim on several occasions.