This photo, taken on April 13, shows North Korean military chief Ri Yong-Ho (L) and North Korean leader Kin Jong-Un (R), seen during a ceremony in Pyongyang.
North Korea's army chief has been relieved of all his posts due to illness, state media said on Monday, in a surprise development that removes one of new leader Kim Jong-Un's inner circle.
Ri Yong-Ho is regarded as one of the key figures who helped support the young, untested leader in the transition following the death in December of his father Kim Jong-Il.
The departure and the quick announcement by the regime were "very unusual", said a spokesman of Seoul's unification ministry handling cross-border affairs, while observers say Ri may have fallen out of favor with Jong-Un.
The 69-year-old became head of the country's 1.2 million-member military -- one of the world's largest -- in 2009 and had been seen often accompanying Jong-Un on visits to military bases in recent months.
The North's official KCNA news agency said a meeting of top officials from the ruling party on Sunday took the decision to relieve him of his posts "for his illness".
He was removed from the "presidium of the politburo", the country's most powerful body with only a handful of members, and the "vice-chairman of the central military commission" of the ruling Workers' Party, it said.
The spokesman for Seoul's unification ministry added to reporters "We are watching the situation with interest," without elaborating further.
The general was one of seven top party and military cadres who accompanied Jong-Un when he walked alongside the hearse carrying the body of Jong-Il during his funeral.
The seven featured in the symbolic moment -- including Jong-Un's powerful uncle Jang Song-Thaek -- were considered central figures in bolstering the regime of the new leader, who is believed to be in his late 20s.
Ri was also seen accompanying Jong-Un as the leader paid tribute in a ceremony in Pyongyang to his late grandfather Kim Il-Sung on the July 8 anniversary of his death in 1994.
Professor Yang Moo-Jin of the University of North Korean Studies in Seoul said he was skeptical about the reason given for the "hawkish" veteran field commander's departure.
"He might have fallen into disfavor with Kim Jong-Un or lost in a power struggle with other military leaders," he said, adding Pyongyang seldom relieved party or military leaders simply for health reasons.
Paik Hak-Soon of Sejong Institute said Jong-Un was seeking to strengthen the communist party's control over the military that has become too powerful for decades under the Songun (army-first) policy of Kim Jong-Il.
"Jong-Un will make sure that now the party keeps the overgrown military under check-- an effort his father started in late 2010 before he died," Paik told AFP.
"Ri is an old fixture from the father's generation. Jong-Un will likely replace him with someone younger and closer to the party...someone he can control more easily," he said.
The North's military has in recent months ratcheted up hostile rhetoric towards South Korea and President Lee Myung-Bak partly in a bid to burnish its new leader's credentials.
The impoverished but nuclear-armed North last month denounced US-South Korean drills near the tense border as a "provocation" and vowed to "further bolster up its nuclear deterrent".
Some 2,000 South Korean and US troops along with jet fighters, tanks and attack helicopters took part in the live-fire exercises to test responses to any North Korean attack.
It was the latest sign of high tensions after the North's failed rocket launch in April, seen by the United States and its allies as an attempted ballistic missile test.