In his continued reign of terror, North Korea’s leader Kim Jong-un executed its defense chief Hyon Yong-chol last month on charges of treason.

Hyon, the head of the People’s Armed Forces, was executed by a firing squad using an antiaircraft gun at a military school in Pyongyang around April 30, South Korea’s top intelligence agency said in its briefing to lawmakers Wednesday.

Pyongyang has not yet announced the purge of Hyon, who was appointed to the No. 2 post in the North Korean military hierarchy last June. According to intelligence officials here, he seemed to have been purged because he was disrespectful to the young ruler. Hyon, 66, was seen dozing off during a military event attended by Kim earlier last month and was said to have disregarded the young leader’s instructions.

Given he was executed shortly after his return home from a weeklong trip to Moscow, Hyon might also have drawn Kim’s wrath because he failed to carry out his assigned missions or gave a false report about the outcome of his meetings with Russian officials. Recent reports said Russia rejected Hyon’s request to purchase sophisticated antiaircraft missiles and called for the North’s denuclearization, probably resulting in Kim canceling his planned visit to Moscow last week.

Hyon’s case was the latest in a series of public executions under Kim’s rule. Since taking power in 2011 upon the death of his father and longtime dictator Kim Jong-il, he has executed about 70 senior officials, including his uncle and mentor Jang Song-thaek.

The young ruler has surpassed his father in unleashing a series of shocking public executions. His cruel behavior may reflect both his impatience with disobedience and concern about a possible challenge to his authority.

At the moment, it seems that his grip on power has been consolidated, with the core elite class in the isolated regime weighed down by fear rather than being driven by anger. It is also difficult for those thinking about launching a rebellion to take an organized move under such harsh oppression.

Still, the possibility cannot be ruled out that the accumulated angst and anger will erupt into extreme action, particularly by some military officers. Kim’s push for misdirected policies without being checked by anyone might also bring catastrophic results.

It is now necessary for Seoul to keep a closer watch over Kim’s moves and prepare for a possible contingency in the North. Precaution should also be heightened against Pyongyang’s habitual pattern of raising tensions to cover its internal instability.