A file photo shows Hyon Yong Chol giving a speech at a national meeting in Pyongyang on December 29, 2012.

Story highlights

North Korean Defense Chief shot by anti-aircraft gun, South Korean media reports

Hyon Yong Chol executed because he was seen "dozing off" at a military event

North Korean official told CNN last week reports of 15 executions of top officials "malicious slander"

Seoul, South Korea CNN  — 

North Korea has publicly executed the country’s defense minister after the regime accused him of treason, according to South Korean news agency Yonhap.

Hyon Yong Chol was killed by firing squad using an anti-aircraft gun at a military school in front of hundreds of people in Pyongyang around April 30, the agency reported, citing a media briefing by the National Intelligence Service at its headquarters in Seoul.

Hyon “was purged for lese majeste” because he was seen “dozing off” during a military event and “did not carry out Kim’s instructions,” the agency said. It wasn’t clear what instructions Hyon failed to carry out.

North Korean leader Kim Jong Un has been accused of ordering the executions of as many as 15 top officials so far this year.

However, during a rare trip to Pyongyang last week, a top official dismissed the allegation as “malicious slander.”

“Especially because they tried to link the alleged statement to the august name of our Supreme Leader Marshall Kim Jong Un,” said Park Yong Chol, the deputy director of the DPRK Institute for Research into National Reunification.

However, he did not deny that executions take place for crimes of treason or subversion: “It is very normal for any country to go after hostile elements and punish them and execute them.

CNN cannot independently confirm the execution claims as North Korea is one of the most closed societies in the world.