March 7, 2014: North Korean leader Kim Jung Un supervises a flight drill of the KPA Air and Anti-Air Force Unit 2620. (Reuters)

Vice Premier Choe Yong-gon, 63, who held the post since June 2014, has not been seen in public since December. If confirmed, the execution marks another report of a gruesome killing ordered by the leader.

A North Korean official who reportedly "expressed discomfort" against leader Kim Jung-un's forestation policy was executed by firing squad sometime in May, Yonhap news agency in South Korea reported.

In May, South Korea's spy agency told the country's lawmakers that Kim executed his defense chief for falling asleep during a meeting and talking back to the young leader. That official was reportedly killed with an anti-aircraft missile.

Due to the clandestine nature of the North Korean government, it is difficult to determine the accuracy of these stories, but the BBC reported that the South Korean government is monitoring the reports.

Koh Yu-hwan, a North Korea expert at Dongguk University in Seoul, said in May Kim Jung-un appears to be using purges to keep the military old guard in check because they pose the only plausible threat to his rule. Koh said Kim could be pushing a "reign of terror" to solidify his leadership, but those efforts would fail if he doesn't improve the country's shattered economy.

In January 2014, The Singaporean Straits Times cited a Beijing-controlled newspaper that said Kim's uncle and five close associates were stripped and fed to 120 starving dogs.

Kim's purges over recent years are seen as efforts to bolster his grip on power. The most notable was in 2013, when Kim executed his uncle and chief deputy, Jang Song Thaek, for alleged treason.