Following North Korea's execution of its young leader's once powerful uncle, South Korea's defense chief on Friday pledged to maintain high military vigilance to deter potential provocations by the unpredictable communist regime.

The latest move comes after Pyongyang's Korean Central News Agency reported that Jang Song-thaek, considered as North Korea's No. 2, was executed on Thursday for treason charges, just four days after he was stripped off all of his posts.

"We will heighten readiness against North Korea as (Jang's execution) can lead to provocations against the South," Kim Kawn-jin said in the parliamentary defense meeting. "This case can be seen as part of the reign of terror by Kim Jong-un as he is seeking to consolidate his power with an iron fist."

Although the ruling Workers' Party can continue to rule the state, Kim said the communist regime could misjudge security situations for several reasons, including a rivalry among the military inner circle to show their loyalty to Kim Jong-un.

"South Korea and the U.S. are closely watching situations inside of North Korea," Kim said, noting his military has not yet raised its surveillance status as no special movement has been detected in the North.

Jang's removal took place less than a week before the second anniversary of the death of leader Kim Jong-il, the current ruler's father, which is expected to give a rare glimpse of the power shift.

Echoing Kim's prediction, Unification Minister Ryoo Kihl-jae said the recent purge is likely to be followed by military provocations, including a nuclear bomb test.

Touching on the speculation that the North will soon conduct their fourth nuclear test, the minister said in a parliamentary meeting, "That is probable. We are keeping an eye on such a possibility."

"I have seen in the past that the North usually curbs internal (agitation) through waging provocations externally," the scholar-turned-official said.

Pyongyang conducted its third nuclear test last February in what the outside world believed to be the final step to completing its development of inter-continental ballistic missiles, in defiance of the United Nations resolutions banning such actions in the North. (Yonhap News)