North Korea warned the world Friday to expect no policy changes under new leader Kim Jong-Un, and threatened retaliation against South Korea for "rubbing salt" into the wounds of its grieving people.

The tough statement came a day after the communist nation ended 13 days of mourning for late leader Kim Jong-Il, and proclaimed his son Jong-Un as new supreme chief at a massive memorial ceremony.

We "solemnly declare with confidence that the south Korean puppets and foolish politicians around the world should not expect any change from the DPRK (North Korea)," said the National Defence Commission (NDC), the top decision-making body.

The North will never have dealings "with the Lee Myung-Bak group of traitors", the NDC said, referring to the South's conservative president in a statement carried on the official news agency and state television.

"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, accusing Seoul's government of insulting behaviour during the mourning period for Kim.

A "sea of tears" shed by the North's army and people would "turn into that of retaliatory fire to burn all the group of traitors".

Despite the bellicose language, analysts said the North was warning the world against any interference during the transition and that the chance of any provocation was low.

The North has moved quickly to elevate the untested son, aged in his late 20s, since his father died of a heart attack on December 17.

He was declared "supreme leader of party and army and people" at the memorial service attended by tens of thousands Thursday, and took the lead role in a huge state funeral the previous day.

The NDC's Korean-language statement Friday referred to the son as "great leader", a title also conferred on his father and grandfather, although the English-language version did not use the phrase.

The world has been watching for any signs of change under the new leader.

His father presided over a 1990s famine which killed hundreds of thousands, pursued a nuclear and missile programme which brought international sanctions and resisted Chinese pressure to reform the crumbling state-directed economy.

Inter-Korean relations have been frosty since Lee took office in February 2008 and linked major economic aid to nuclear disarmament.

Ties turned icy after Seoul accused Pyongyang of torpedoing a warship in March 2010 with the loss of 46 lives. The North denied involvement but shelled a South Korean island in November 2010, killing four people.

However, Seoul's response to Kim's death was seen as conciliatory even by domestic political opponents.

It expressed sympathies to the North's people but not the regime, and allowed South Koreans to send pre-approved condolence messages northwards.

However it permitted only two private mourning delegations to visit Pyongyang and sent no government representative.

The North has repeatedly blasted the "inhuman" response by the South, and rapped Seoul's decision to briefly order troops on alert after Kim's death.

On Friday it also vehemently criticised a cross-border leaflet launch staged by defectors on Wednesday, the day of Kim's funeral.

The South's government was "hurting the grief-stricken compatriots and rubbing salt into their wounds", it said, while expressing hope of better ties under a future government in Seoul.

Yang Moo-Jin, of Seoul's University of North Korean Studies, said the North was demanding that Seoul quickly accept its new leadership.

"Cross-border relations will remain icy for the time being. However, the possibility of military provocations by North Korea is low," he told AFP.

"This is a message to the world that there will be no change in its policy and system. It is warning the outside world not to interfere with its internal policy."

Kim Yong-Hyun, of Seoul's Dongguk University, also ruled out major provocations.

"The statement is strong, but its harsh rhetoric does not necessarily mean North Korea will sever ties with the outside world. It will try to improve relations with the United States."

The North, Kim said, was strongly urging the South to change its policy and the statement was also intended to strengthen internal solidarity.

Analysts have said the memorial was designed as a show of confidence in Jong-Un.

Lee, in a New Year message Monday, is expected to clarify his approach to the new regime. The South Korean president stressed after Kim's death that his country is not hostile to its neighbour.