The dispatch on North Korean state media came just hours before the nation was to hold the largest Workers' Party convention in 30 years, a meeting where Kim Jong Un was expected to make his political debut.
The much-delayed meeting in Pyongyang has begun, China's state-run news agency Xinhua reported late Tuesday morning, citing Minju Choson, a government-run North Korean newspaper. The report could not be verified.
The announcement that the elusive Kim Jong Un was promoted to general, along with his aunt and four others, marked the son's first ever appearance in North Korean state media.
"Kim Jong Un's promotion is the starting point for his formal succession to power," said Kim Yong-hyun, a North Korea expert at Seoul's Dongguk University.
In another notable promotion, Kim Jong Il also made his elder sister, Kim Kyong Hui, a general in the Korean People's Army, the official Korean Central News Agency said.
Kim Jong Il, now 68, is believed to have been grooming a son to carry the Kim dynasty into a third generation since suffering a stroke two years ago.
He himself took over leadership in 1994 when his father, North Korea founder Kim Il Sung, died of heart failure in what was communism's first hereditary succession.
However, with the son still in his 20s and inexperienced, the 64-year-old sister may be tapped to oversee a transfer of power if the leader dies before the son is ready to take over, experts say.
"There is a possibility that she could play the role of a coordinator to make sure the power succession goes smoothly," said Cheong Seong-chang, a senior fellow at the Sejong Institute think tank near Seoul.
She and her husband, Jang Song Thaek, who is vice chairman of the all-powerful National Defense Commission, are likely to act as guardians for the young Kim during his rise to power, analysts said.
The question of who will take over from the authoritarian leader is important to regional security because of North Korea's active nuclear and missile programs and concerns of chaos in the case of upheaval in the impoverished country.
The two Koreas remain at war and divided by a heavily fortified border because their three-year conflict ended in a truce, not a peace treaty, in 1953.
Very little is known about Kim Jong Un, believed to be 28 and schooled for several years under a pseudonym in Switzerland.
He graduated from Kim Il Sung Military University, a key attribute needed for leading a country operating on a "songun," or "military first," policy, said analyst Paik Hak-soon of the Sejong Institute.
He has two older brothers, Kim Jong Nam and Kim Jong Chol, but the youngest is said to be most like his father.
Kenji Fujimoto, who said he worked for years as Kim Jong Il's sushi chef, wrote in a memoir that Jong Un was sharp, competitive and even "ruthless" — and his father's favorite.
However, there is no known photo of Kim Jong Un, and until recently the South Korean government wasn't sure how to spell his name because he had not appeared in any state media.
US Assistant Secretary of State Kurt M. Campbell said in a conference call late Monday that Washington was "watching developments carefully" and was working to interpret the announcement's significance.
There was a celebratory air in the streets of Pyongyang, which were festooned with flags and placards marking the Workers' Party meeting.
In Pyongyang, one expert called the gathering a significant occasion for the North Korean people.
"This meeting of the delegates is an important occasion for further strengthening the solidarity of our army, our party, and our people, who are rallying behind the great Gen. Kim Jong Il," Kim Chang Gyong, an assistant professor at North Korea's Academy of Social Sciences, told broadcaster APTN.
The Workers' Party meeting had been scheduled to take place in early September but appeared to be have been delayed by several weeks. State media did not provide a reason.
North Korea, which struggles to feed its people, has also been coping with devastation from flooding and a typhoon that left dozens dead, according to state media.
