|Kim Kyok-sik (left) and Jang Jong-nam|
The official KCNA news agency on Monday introduced Jang Jong-nam as the new minister of the People's Armed Forces.
Jang was among senior officials alongside leader Kim Jong-un who watched a performance by a song-and-dance ensemble of the Internal Security Forces, KCNA said.
As recently as May 3, it was Kim Kyok-sik who accompanied Kim Jong-un.
It is unclear whether Kim Kyok-sik took the fall for the recent months of unsuccessful saber-rattling that only prompted the North's sole ally China to tighten sanctions.
"We'll have to wait and see whether it was a demotion or just a replacement," a security official in South Korea said. "If he'd made a minor mistake, Kim Kyok-sik would have kept his post but been demoted in rank, so he must have made a pretty big mistake."
Kim Kyok-sik was the commander of the infamous Fourth Army Corps that controls the area around the Northern Limit Line. There his troops provoked a naval skirmish near Daecheong Island in November 2009, sank the South Korean Navy corvette Cheonan in March 2010 and shelled Yeonpyeong Island in November the same year.
After the shelling of Yeonpyeong Island, Kim was reprimanded by the Politburo for failing to respond properly to the South Korean counterstrike. But he popped back up as armed forces minister in November last year.
Nothing is known about his successor Jang except that he had been the commander of the First Army Corps, which controls the frontline area in Kangwon Province, and that he is in his 50s.
Kim's ouster means that all three top North Korean military posts, the chief of the Army's General Staff, the chief of the General Political Bureau, and the minister of the People's Armed Forces, have gone to a slightly younger generation in their 50s and 60s.
Some believe new leader Kim Jong-un is purging the powerful military of superannuated hawks associated with his father's "military-first" regime.
"Unlike his father who let senior military leaders stay in their posts until they grew old and died, Kim Jong-un has wrought generational shift in key posts since he took power," the South Korean security official added. "Maybe he's trying to get out of his father's shadow."