North Korea has accused South Korea of an "intolerable" response to Kim Jong-Il's death, a blast that came as diplomats at the United Nations held a mass boycott of a tribute to the late leader.

Pyongyang's official media says millions are braving bitter cold to mourn the "Dear Leader" after his sudden death on December 17 -- and South Koreans are welcome to join the condolences.

Its Uriminzokkiri website said any mourning delegations from the South would be accepted, and lashed out at the Seoul government's "inhuman" decision to allow only two such visits.

The world is closely watching Kim's chosen successor -- his untested youngest son Kim Jong-Un -- for clues about the future direction of the impoverished but nuclear-armed state.

Uriminzokkiri's comments, dated Thursday and seen Friday, seemed to suggest no immediate change in frosty cross-border ties.

The South blames its neighbour for two deadly border attacks last year but has taken a conciliatory stance since Monday's announcement of Kim's death.

Seoul's government sent its sympathies to the North's people, scrapped a controversial plan to display Christmas lights near the border and announced that South Koreans could send pre-approved condolence messages northwards.

It said there would be no Seoul government delegation to offer condolences but authorised two groups to pay respects in Pyongyang.

By law, Seoul's unification ministry must authorise all contacts between South and North Koreans. The two sides have stayed technically at war since their 1950-53 conflict.

Uriminzokkiri said all South Korean delegations wishing to visit Pyongyang to mourn Kim "with a warm heart" would be accepted. It was unclear whether they would be allowed to stay on for the actual funeral next Wednesday.

But it said the South was blocking such visits and trying to escalate confrontation by strengthening security. "These are intolerable actions of mockery and insult against our dignity."

The website described Seoul's ban on most delegations as an "unacceptable, uncivilised and inhuman action" which could have a "significant impact" on relations.

In an apparent reference to the South's failure to send an official delegation, it also accused Seoul of disrespect.

"We will keep in mind those who do not understand even the most basic actions of respect and humanity and who insult our dignity, and we will make them pay a very expensive price for that for years to come," it said.

Seoul's unification ministry said its decision was unchanged. Only the families of former president Kim Dae-Jung and former Hyundai Group chairman Chung Mong-Hun would be allowed to visit.

Kim Dae-Jung and Kim Jong-Il held the first-ever North-South summit in 2000 and the Hyundai Group pioneered cross-border business exchanges.

Jeung Young-Tae of the South's Korea Institute for National Unification, told AFP the North was "trying to foster division" with its offer and would exploit any such South Korean mourners for propaganda purposes.

At the United Nations, the North's ambassador called for a minute of silence Thursday in a tribute to Kim -- but the United States, most European nations, Japan, South Korea and others boycotted it.

"This is a man who is responsible for probably tens of thousands of deaths. He is not a model for the UN," said one European diplomat. Barely a third of the UN General Assembly's 193 members were present for the tribute.

During his 17-year absolute rule, Kim presided over a 1990s famine that killed hundreds of thousands. Severe food shortages continue and rights groups say tens of thousands are held in political prison camps.

Kim also pursued a nuclear and missile programme which brought sanctions on his country.

The North quit six-nation disarmament talks in 2009 but diplomatic efforts to restart them had appeared to make progress until Kim's death.

South Korea and China have agreed to work together to "swiftly reinvigorate" efforts to revive the talks, Seoul's chief nuclear envoy Lim Sung-nam said Friday on his return from talks in Beijing.

The North has been burnishing the image of both its past and present leaders with fulsome tributes and claims that even Mother Nature mourns Kim Jong-Il, who died of a heart attack at age 69.

His body lies in state in a glass coffin at a Pyongyang memorial palace, where hundreds of mourners including his son and heir have shed copious tears.

The official state news agency said a total of 43,929,000 mourning visits had been made to various commemorative sites nationwide between noon Monday and Wednesday evening. The country's population is around 24 million.

It reported continuing natural phenomena across the nation, such as simultaneous blinding blue flashes, thunder and snowfall near the border city of Kaesong.

"Witnessing this, citizens of the city said that the demise of Kim Jong-Il was so heart-rending that even the sky seemed to writhe in grief," it said.