North Korea on Sunday lashed out at South Korea for a perceived lack of respect towards Kim Jong-Il, as it reported more scenes of mass grieving in the isolated communiist state for the late leader Saying the whole world is in mourning for "a peerlessly great man", the North for the second time in three days blasted the South over its response to Kim's sudden death on December 17.
There would be "unpredictable catastrophic consequences" for cross-border relations unless Seoul eases restrictions on condolence visits by South Koreans to Pyongyang, it said.
The South blames its neighbour for two deadly border incidents last year, but has taken a generally conciliatory stance since Monday's shock announcement that Kim had died of a heart attack two days earlier at age 69.
The Seoul 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.
But the authorities, who by law must approve all contacts with Pyongyang, are allowing only two private delegations to visit the North to pay respects and are not sending an official team.
Following the South's announcement, the North said it would open its borders to all South Koreans who wish to travel to Pyongyang.
"The South Korean authorities should bear in mind that their obstructions will entail unpredictable catastrophic consequences to the north-south relations," a spokesman for the Committee for the Peaceful Reunification of Korea, a state body overseeing cross-border relations, told the official news agency.
The Seoul authorities' "unethical acts bereft of elementary etiquette and compatriotism have touched off unanimous outrage and wrath among Koreans and all other people of the world", the spokesman said.
Despite the tough rhetoric, analysts generally do not expect shows of military force as the new regime headed by Kim's son Jong-Un settles in.
The transition was high on the agenda when Japan's Prime Minister Yoshihiko Noda held talks with Premier Wen Jiabao at the start of his first visit to China as premier.
"Kim Jong-Il passed away, so we are currently facing a new situation in East Asia," Noda said.
"And on this issue it is very timely to exchange views with the host of the six-party (nuclear disarmament) talks and the country with the most influence on North Korea."
The negotiations aimed at scrapping North Korea's atomic weapons programme group Japan, China, the two Koreas, the United States and Russia and have been at a standstill since December 2008.
Diplomatic efforts to revive them had seemed to be making progress before Kim's death.
The North's state media has been heaping praise on both the late father and the son for the past week.
Jong-Un has laid on extra hot drinks and medical care for streams of mourners visiting various sites in the bitter cold, its news agency said.
On Saturday the ruling party hailed Jong-Un as "supreme commander", the latest sign that the untested youth in his late 20s is tightening his grip on power.
But the Kim dynasty's newest ruler remains a figure of mystery to the world, which is seeking clues to future policy in the nuclear-armed nation.
Fresh TV footage aired Sunday showed Jong-Un and other top military and party officials paying respects the previous day at the bier bearing the glass coffin of his late father.
They included Jang Song-Thaek, Jong-Un's uncle and a likely key figure in the succession process, wearing a military uniform with the insignia of a general.
The South's Yonhap news agency said it was the first time Jang had been shown in public wearing a military uniform, triggering speculation he might have been appointed a general after Kim's death.
The North's news agency said participants pledged the military's loyalty to the son under the slogan "Let us defend with our very lives the Party Central Committee headed by respected Comrade Kim Jong-Un!"
Ruling party newspaper Rodong Sinmun said more than 10,000 workers and soldiers had made pilgrimages as of Saturday to Mount Paekdu on the Chinese border, the supposed birthplace of Kim Jong-Il.