North Korea has reportedly informed its embassies and overseas missions of the execution of its defence chief Hyon Yong Chol.

South Korea's National Intelligence Service (NIS) had reported last month that the North Korean army chief was executed with an anti-aircraft gun for falling asleep at a meeting with Kim Jong-un, though doubts had emerged after Hyon Yong Chol "appeared" in propaganda films even after the reports.

However, North Korea has now confirmed to its embassies that the army chief was indeed executed for "disobedience", South Korea's Chosun Ilbo media reported, citing a source from Beijing.

Hyon Yong Chol was reportedly executed after he failed to answer a question posed by Kim Jong-un at a meeting as he had allegedly fallen asleep.

"Kim believes dozing off or getting distracted in a meeting is worse than opposing his decisions," the source told the newspaper.

Hyon Yong Chol was last seen publicly at a security conference in Moscow in April.

The report also said that several senior military officers had "disappeared" since the army chief's execution.

Speculations have now begun over an army general who appeared with Kim Jong-un at an event, with reports suggesting that he could be the new army chief instated in place of Hyon Yong Chol.

North Korea's state media KCNA reported on Monday that Kim had attended a military art performance, and listed the name of four-star army general Pak Yong-sik before that of Army Gen. Ri Yong-gil, chief of the General Staff of the KPA, which is said to be an indication of the former being promoted to the post of the defence chief, Yonhap news agency reported.