The regime of North Korean dictator Kim Jong Un used an anti-aircraft gun to execute the country's defense minister, Hyon Yong Chol, reports South Korea's Yonhap newswire, which cited Seoul's National Intelligence Service.

The South Korean spy agency said the immediate cause of Hyon's killing was not because the 66-year-old chief of the North Korea's People's Armed Forces may have been trying to start a rebellion against Kim, but rather he had dozed off and failed to carry out Kim's orders, according to Yonhap.

The young dictator is believed to have ordered the executions of a number of top officials in recent years, most notably that of his uncle, Jang Song Thaek, whom he accused of treason in 2013.

"The report, if true, would starkly illustrate the brutal extent to which the young North Korean leader is going to consolidate power," the Washington Post commented.

South Korean lawmaker Kim Gwang-lim told CNN that, according to the National Intelligence Service, Hyon was executed without trial and within two to three days of being arrested.

Reports suggest that the killing took place "around April 30" and that the minister was executed by firing squad using an anti-aircraft gun in front of hundreds of people at a military school in Pyongyang.

"If the dates are correct, they suggest Hyon's fall from grace was swift and decisive," CNN judged.

This is not the first time someone has been executed with anti-aircraft weapons in the Hermit Kingdom. A report by Human Rights in North Korea purports to show satellite image evidence that shows the country has been conducting executions with the heavy weapons for some time.

Michael Madden, who runs the North Korea Leadership Watch blog, told the Washington Post that Wednesday's report seemed genuine and marked the latest in a slew of "personnel changes" in North Korea.

"Hyon was a critical guy," Madden said. "I don't think there is a stability issue, but I think there are some internal dynamics going on," he added.

Last month, Hyon had led a North Korean delegation to Moscow for a seminar on global security, CNN recalled. A spokesman for South Korea's Unification Ministry noted that Seoul considered the execution to be another display of "fear politics" in the North.