North Korea on Monday added an important title to the fast-growing credentials of its untested new ruler, referring to the youngest son of late leader Kim Jong-il as head of a key ruling party body.
In a move that experts said shows the anointed successor is on track to take full control of the secretive nation, the ruling party newspaper hailed Jong-un as head of its Central Committee.
"Let's stake our lives to safeguard the party's Central Committee led by dear comrade Kim Jong-un," Rodong Sinmun said.
Jong-un, in his late 20s, has already been touted as "great successor" and "supreme commander" of the military since his father died on December 17 of a heart attack at the age of 69.
Usually the head of the Central Committee — a top decision-making body — is also its general secretary, a position previously held by Kim Jong-il.
"Jong-un has not officially taken over as general secretary, but he is expected to inherit it and other posts held by his father," Dongguk University professor Kim Yong-hyun told AFP.
The late Kim also chaired the all-powerful National Defence Commission and headed the 1.19 million-strong military.
Officially, Jong-un's current highest post is vice-chairman of the party's Central Military Commission.
The North's official media heaped more praise on Jong-un, describing him as a "tender-hearted man" who sent hot, sweet drinks to mourners braving freezing conditions in the capital Pyongyang.
The isolated state is making final preparations for what is expected to be an elaborate funeral for Kim on Wednesday that will be closely watched for clues about the powers at the side of the new ruler.
Kim's death dominated a visit by Japan's Prime Minister Yoshihiko Noda to China, where he met President Hu Jintao on Monday, a day after talks with Premier Wen Jiabao.
China is North Korea's closest ally, and Noda has said safeguarding the peace and stability of the Korean peninsula is "in the common interest" of the two regional powers.
In South Korea, Lee Hee-ho, the 89-year-old widow of late president Kim Dae-jung, and Hyundai Group chairwoman Hyun Jung-eun left on a private visit Monday to express their condolences.
They crossed the world's last Cold War frontier and travelled overland to Pyongyang where they were to meet officials during their two-day trip. They will not stay for the funeral.
"I hope that our visit to the North will help improve South-North relations," Yonhap news agency quoted Lee as saying before she crossed over with her aides.
It was unclear whether they would meet Jong-un.
Kim Dae-jung and Kim Jong-il held the first-ever inter-Korea summit in 2000 and Hyundai pioneered cross-border business projects.
A South Korean left-wing activist also left Saturday for North Korea via Paris and Beijing to pay her respects, her colleagues said, despite Seoul's ban on visits other than the trip by the former first lady and Hyundai chief.
The North on Sunday lashed out at South Korea for its response to Kim's death, warning of "catastrophic consequences" for relations unless Seoul eases restrictions on condolence visits by South Koreans.
The South blames its neighbour for two deadly border incidents last year, but has taken a generally conciliatory stance since the shock announcement on November 19 that Kim had died of a heart attack two days earlier.
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.
The two Koreas have remained technically at war since the 1950-1953 Korean conflict ended only in a ceasefire.
A group of pro-North Korean activists said they planned to set up an altar in Seoul to mourn Kim's death despite conservative opposition.
They will display Kim's photo with flowers in downtown Seoul Monday to "share sorrow with compatriots in North Korea," said their leader Yon Ki-hor.