SEOUL—North Korea’s defense minister has been executed by antiaircraft fire for disloyalty and showing disrespect to dictator Kim Jong Un, senior officials from Seoul’s National Intelligence Service told South Korean lawmakers in a closed hearing Tuesday.

Defense Minister Hyon Yong Chol allegedly fell asleep during military events and talked back to the leader, the officials told the Intelligence Committee of South Korea’s National Assembly, according to a person familiar with the briefing.

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