Jong-Un had already been declared "supreme leader" of the country during memorial ceremonies for his late father Kim Jong-Il on Thursday, as the nation ended 13 days of mourning.[break]
"The dear respected Kim Jong-Un...assumed the supreme commandership of the Korean People´s Army at the behest of leader Kim Jong-Il," according to the official news agency.
It said the decision was proclaimed Friday at a meeting of the political bureau of the ruling communist party´s central committee.
Jong-Un, aged in his late 20s, inherits the world´s fourth largest armed forces of 1.2 million and a national policy known as Songun that prioritises their needs over those of civilians.
UN agencies say a quarter of the population urgently needs food aid, the ailing economy is struggling with shortages of power and raw materials and a nuclear and missile programme has brought international sanctions.
But the regime stressed Friday it would not change course.
We "solemnly declare with confidence that the south Korean puppets and foolish politicians around the world should not expect any change", said a statement from the National Defence Commission, the top decision-making body.
The North said it would never have dealings with the conservative South Korean government, which it designates as "traitors", and harshly criticised Seoul for perceived slights during the mourning process for Kim.
"We will surely force the group of traitors to pay for its hideous crimes committed at the time of the great national misfortune," it said.
Pyongyang renewed the attack Saturday, threatening to "settle accounts" with President Lee Myung-Bak´s government unless it apologises for the alleged insults.
"He (Lee) is the worst type of anti-reunification element, traitor and pro-US fascist maniac steeped in extreme bitterness towards compatriots and confrontation hysteria to the marrow of his bones," the Committee for the Peaceful Reunification of Korea said in a statement.
The North "is left with no option but to finally settle accounts with the Lee group unless it apologises for the above-said crimes", it said.
Despite the bellicose language, analysts said the North was trying to close ranks against a purported enemy and warning the world against any interference during the transition.
They said the chance of any provocation was low in the near future.
Lee´s government expressed sympathy for North Korea´s people but not the regime after Kim´s death and allowed only two private mourning delegations to visit Pyongyang.
Activists launched propaganda leaflets across the border into the North on the day of Kim´s funeral. Seoul says it cannot legally ban the launches.
Jong-Un was made a four-star general in September 2010 and given important party posts as his father groomed him for the country´s second dynastic succession.
He was swiftly proclaimed "great successor" after Kim senior died of a heart attack on December 17 at the age of 69.
North Korea also announced that it would issue gold and silver coins to mark the 20th anniversary of Kim Jong-Il´s appointment as military commander.
It said the coins would mark the former leader´s "immortal achievements" of making the country an invincible nuclear-armed military power.
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