Succession touted as reason for Kim's show of strength

Hidden from the public eye, even in North Korea, the youngest son of the dictator Kim Jong-il has for months been the focus of discussions about who might next lead the impoverished state.

Many analysts believe the North's internationally condemned nuclear test on Monday was partly aimed at boosting the standing of the 67-year-old leader, who suffered a stroke last year, to give him more leverage in anointing an heir. That heir is believed to be his third son, Kim Jong-un. There is no confirmed photograph of him as an adult and his age is unclear. He was born either in 1983 or early 1984.

There is a question too over whether his late mother, a Japanese-born professional dancer called Ko Yong-hui, was Kim Jong-il's official wife or mistress – an issue that might weigh on his legitimacy to replace his father.

Even by intensely secretive North Korean standards, remarkably little is known about the potential heir, whose youth could also prove problematic in a society that adheres closely to the importance of seniority.

Kim Jong-il was very publicly named heir by his father, Kim Il-sung, but he has studiously avoided repeating the process. None of his three sons is mentioned in state media.

Kenji Fujimori, in a book on his time as chef to the ruling household, said that of the three sons, the youngest Kim most resembles his father. Kim Jong-un is also reported to have a ruthless streak and the strongest leadership skills of the three boys. and, perhaps more importantly, he is thought to be his father's favourite.

Park Syung-je, a Seoul-based analyst with the Asia Strategy Institute, said he believed Kim Jnr had the backing of Jang Song-taek, effectively the country's No 2 leader.

In April, Kim Jong-il promoted Mr Jang, his brother-in-law, to the powerful National Defence Commission, which many analysts took to be an attempt to establish a mechanism for the eventual transfer of power, with Mr Jang as kingmaker.