North Korean leader Kim Jong-Un led thousands of officials Sunday in a memorial ceremony for his late father and ex-ruler Kim Jong-Il, days after a successful long-range rocket launch.

The ceremony followed a mass rally two days earlier hailing the launch of the three-stage rocket, a move which was condemned by the UN Security Council and seen by many countries as a disguised ballistic missile test.

Kim Jong-Il (pic) who ruled the communist state for 17 years, died of a heart attack on December 17 last year.

His youngest son Jong-Un immediately took over, the second dynastic succession by the Kim dynasty which has ruled the isolated country for more than six decades with an iron fist and a pervasive personality cult.

Officials in black suits and uniformed military leaders convened in a cavernous stadium in the capital Pyongyang Sunday morning for the hour-long memorial event, which was televised live on state TV.

Jong-Un, stone-faced and clad in a black Mao suit, sat on stage with dozens of other top officials against the backdrop of a giant red flag featuring a large portrait of a smiling Kim Jong-Il.

"The heart of the great leader stopped beating but Comrade Kim Jong-Il lives with us forever... to give blessings for the bright future of our people," the ceremonial head of state Kim Yong-Nam said in a speech.

"The successful launch of our Kwangmyongsong-2 satellite is also another victory achieved by our military and people, by faithfully following the teachings of the great leader (Kim Jong-Il)," he said.

It was unclear what memorial events were scheduled on Monday, the anniversary day.

The North said the apparently successful launch -- its second after a much-heralded but botched mission in April -- was a scientific project to put a weather satellite into orbit.

But the United States and other nations viewed it as a disguised ballistic missile test banned under UN resolutions triggered by its past nuclear tests in 2006 and 2009.

The Security Council Wednesday condemned the launch and said members "will continue consultations on an appropriate response".

The impoverished but nuclear-armed nation apparently timed the launch to mark the death anniversary and to drum up more support for the young and inexperienced Jong-Un.

Choe Ryong-Hae, the head of the political bureau at the North's military, vowed to "hit back immediately" if rival South Korea or the United States provokes the nation, and reaffirmed loyalty to the young leader.

"Our whole army stands ready for battle under the teachings of Kim Jong-Un while the US and South's enemy forces are going amok to destroy our system," he said in a speech.

"It is our firm determination to hit back immediately at provocations...and we solemnly pledge again to faithfully serve our dear supreme commander (Jong-Un)," Choe said to big applause from the crowd.

Mass rallies are being staged nationwide to celebrate the rocket launch, the ruling party newspaper Rodong Sinmun said Sunday.

Officials, students, workers and soldiers in three northern provinces rallied Saturday to give speeches and sing songs in memory of the late ruler and to praise his son for leading the successful launch, it said.