North Korea's defense chief has become the latest key figure in the isolated country to be purged under Kim Jong-un's leadership, according to South Korea's spy agency Wednesday, Anadolu reported.
People's Armed Forces Minister Hyon Yong-chol was executed using "an anti-aircraft gun" late last month, according to an official from Seoul's National Intelligence Service (NIS) cited by local news agency Yonhap.
He is reported to have failed to follow orders, and fallen asleep at an event attended by Kim.
The 66-year-old Hyon was at the 4th Moscow International Security Council as recently as April 16, and had stood alongside Kim at Pyongyang's Kumsusan Palace of the Sun in February to mark the birthday of the leader's late father, Kim Jong-il.
South Korea's NIS claims around 70 senior officials have been executed as part of Kim Jong-un's consolidation of power since he assumed office at the end of 2011 - most notably the leader's uncle, Jang Song-thaek, in 2013.
"As key officials have voiced more complaints, Kim has deepened a reign of terror by purging them in negligence of proper procedure," the NIS official was quoted as telling a gathering of reporters.
Seoul's spy agency said it believes there are "growing doubts about Kim's leadership among North Korean ranking officials."
Pyongyang is yet to confirm the execution of Hyon, but the case raises once more the North's methods of carrying out capital punishment.
The NIS has denied a report out of the United States suggesting that Kim's aunt was poisoned last year, and claims that Kim's uncle was fed to a pack of dogs were later discredited.
But there have been longstanding rumours of execution by powerful weapons.
Satellite images taken last October, and recently released by the Committee for Human Rights in North Korea and AllSource Analysis, suggest that Pyongyang does use anti-aircraft guns for executions.