Jang Sung-taek’s execution in North Korea has rekindled fears of instability in the secretive nuclear-armed state.
South Korean defense chief Kim Kawn-jin promised “heightened readiness” after the purge of Jang Sung-thaek.
Kim Kawn-jin said the execution could be seen as part of a “reign of terror” by the North Korean leader.
Jang Sung-taek, Kim Jong-un’s uncle, was executed for “acts of treachery” after appearing before a military trial.
He was dramatically removed from a special party session by armed guards earlier this week.
South Korean Unification Minister Ryoo Kihl-jae warned that the purge could be followed by military moves from Pyongyang, including another nuclear test.
He told lawmakers that “the North usually curbs internal (agitation) through waging provocations externally”.
North Korea carried out its third nuclear test in February, to widespread international condemnation.
As tensions rose, Pyongyang threatened attacks on Japanese, South Korean and US military targets in the region.
China, North Korea’s ally and neighbor, described Jang Sung-taek’s execution as an “internal matter”.
“As a neighboring country, we hope for North Korea to maintain stability…” South Korean foreign ministry spokesman said.
Victor Cha, a former senior White House adviser on Asia, warned that Kim Jong-un’s purge could spread further than Jang Sung-taek.
“If he has to go as high as purging and then executing Chang, it tells you that everything’s not normal,” Victor Cha said.
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