North Korean ruling party promotes son of Kim Jong-il
The youngest son of North Korean leader Kim Jong-il has been appointed to two key party posts, in a move widely seen as part of a gradual transfer of power.
Kim Jong-un was named vice-chairman of the Central Military Commission of the Workers' Party and was appointed to its central committee, state media said.
Kim Jong-il, thought to be in poor health, was re-elected as leader at the party's first congress for 30 years.
The US said the significance of the promotions was not yet clear.
"I would suppose this is perhaps the ultimate reality show unfolding in North Korea, and we are simply watching this very closely," said state department spokesman PJ Crowley.
Chinese President Hu Jintao sent congratulations to Mr Kim on a successful party conference - but did not mention Kim Jong-un's promotion.
Mr Hu said China would "always handle, maintain and boost China-DPRK [North Korea] relations from a strategic height and a long-term perspective... despite the ups and downs of the international situation".
The US and China, the North's only real ally, have held regular talks with Pyongyang over its nuclear programme in recent years, and the UN has placed sanctions on the North over the issue.
Kim Jong-un is Kim Jong-il's third son and had already been identified as the most likely successor to the Communist dynasty started by his grandfather, Kim Il-sung, in 1948.
The BBC's John Sudworth in the South Korean capital Seoul says his rise is remarkable, even by the standards of one of the world's most totalitarian states.
He says there can now be little doubt that Swiss-educated Kim Jong-un, who is thought to be 27 years old, has been chosen to eventually take over from his ailing father.
Among the other promotions given to him at the current party conference, the younger Mr Kim was also given the rank of a four-star general.
The military, backed up by a standing army of 1.2 million troops, is said to run the country's political process through the National Defence Commission, chaired by Kim Jong-il.
The leader's sister and her husband were also given promotions, with analysts saying it is likely that they are being charged with helping to ease the transfer of power to Kim Jong-un.
The Workers' Party has been holding its first meeting since a 1980 congress when Kim Jong-il was promoted.
The 68-year-old leader, who has been in power since his father died in 1994, is said to have suffered a stroke two years ago.
Under his rule, the country's isolation from the outside world has become entrenched.
Mr Kim has built up a personality cult around his family, while North Korea's economy has all but ceased to function and its people suffer from frequent food shortages.