Hundreds of officials watched Hyon's execution on April 30, Han Ki-Beom, the deputy director of the National Intelligence Agency (NIS), told a parliamentary committee, the Yonhap news agency reported.
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 Jong-Un on several occasions, Yonhap said.
The Yonhap report was based on a briefing by a ruling Saenuri party lawmaker who attended the parliamentary committee meeting.
In North Korea, the defence minister is mainly in charge of logistics and international exchanges. Policy-making is handled by the powerful National Defence Commission and the party Central Military Commission.