North Korea's defence chief has reportedly been executed by anti-aircraft gun as punishment for falling asleep at an event attended by Kim Jong-Un.

Defence minister Hyon Yong Chol (66) was charged with treason after having shown "disrespect" to Mr Kim at the military event and allegedly talking back to him.

The claims were made by South Korea's National Intelligence Service (NIS) to politicians in a closed-door parliamentary briefing.

It said hundreds of officials watched the execution in late April at a shooting range at the Kanggon Military Training Area, north of Pyongyang.

He was killed by a firing squad using anti-aircraft guns, South Korea's Yonhap news agency reported.

Hyon, who had been in the role for less than a year, was also thought to have voiced complaints against Mr Kim and not followed his orders several times.

He was arrested late last month and executed three days later without legal proceedings, the NIS said.

South Korea's spy agency has a patchy record of tracking developments in North Korea and information about the isolated state is often impossible to confirm.

In the past, when rumours have circulated about senior officials possibly being killed, they have soon appeared on North Korean television to show the reports are wrong.

However, Hyon has not appeared on TV since reports of his death.

The news comes after South Korea's spy agency said last month that Mr Kim had ordered the execution of 15 senior officials this year as punishment for challenging his authority.

Kim Jong-Un, who took power in 2011 after the death of his father Kim Jong-Il, has conducted a series of purges to try to strengthen his grip on power.

"Bodies would be nearly pulverised"

The most high-profile was the 2013 execution of his uncle, once considered the second most powerful person in the regime.

Jang Song-Thaek was killed after being accused of being a traitor and allegedly living a "dissolute and depraved life" that involved drug use, womanising and gambling.

A US-based North Korea human rights group also believes executions involving six ZPU-4 anti-aircraft guns took place at the Kanggon Military Training Area in October.

The Committee for Human Rights in North Korea (HRNK) believes the powerful guns, which have a range of 26,000ft, were fired at the target from just 100ft.

"Bodies would be nearly pulverised. The gut-wrenching viciousness of such an act would make 'cruel and unusual punishment' sound like a gross understatement," said the HRNK.

It published satellite images that it said indicated a viewing area had also been set up for party officials and VIPs to watch the killings.

Around 70 officials are believed to have been executed since Mr Kim took power, the Yonhap news agency cited the NIS as saying.

John Everard is a former British ambassador to North Korea.

He told the Pat Kenny Show here on Newstalk if this latest killing is accurate, it is not totally surprising.