North Korean leader Kim Jong-Un said Wednesday the Korean peninsula would be engulfed by "massive nuclear disaster" if war breaks out there again, warning the US it will not be safe in the event of a conflict.

"If the war breaks out again in this land, it will bring about a massive nuclear disaster and the US will never be safe," Kim said in his New Year message, broadcast on state TV.

"We are faced with a dangerous situation in which a small, accidental military clash can lead to an all-out war," he said.

Kim added he would not beg for peace and vowed to protect the impoverished but nuclear-armed North with strong self-defence measures against enemies.

The young leader also hailed the recent execution of his powerful uncle as a "resolute action," labelling Jang Song-Thaek "scum".

"Our party took resolute action to remove... scum elements within the party last year," Kim said, accusing Jang of trying to build his own powerbase within the ruling party.

"Our party's timely, accurate decision to purge the anti-party, anti-revolutionary elements helped greatly cement solidarity within our party," he said.

It was the first time Kim has publicly criticised his disgraced uncle, who was executed on December 12 on charges including treason and corruption.

Jang, 67, played a key role in cementing the leadership of the inexperienced Kim Jong-Un, who took power after the death of his father and longtime ruler, Kim Jong-Il, in December 2011.

But Jang's growing political power and influence drew resentment from his nephew barely half of his age, analysts said.