Kim appointed Kim Jong-chol as deputy chief of a leadership division in the ruling Workers’ Party, said The Mainichi Shimbun, quoting sources close to the North Korean government. 

The appointment makes Jong-chol the most likely to succeed his father, given that Kim Jong-il once held the same post and his two other sons have no key responsibilities. Jong-chol is believed to be 26. 

Kim’s succession is one of the most closely guarded secrets in the world’s only communist dynasty and is a constant subject of speculation for the outside world. 

The Mainichi quoted one source as saying Jong-chol was likely to be officially named successor when he reaches 32, the same age as Kim Jong-il was when he publicly emerged as heir to his late father, state founder Kim Il-sung. 

Kim Jong-il, 65, has three known sons, Jong-nam, Jong-chol and Jong-un, by two women. 

The eldest, Jong-nam, was deported from Japan in 2001 for trying to enter the country on a forged Dominican Republic passport. 

He reportedly fell out of favour at home over the incident and has since been the target of two assassination attempts, South Korean media reported, citing intelligence sources. 

Second-born Jong-chol, the son of Kim’s second mistress, Ko Yong-hi, has been tipped as the most likely successor, although there has been speculation that he suffers from a disease that causes him to produce excessive female hormones. 

Japan’s Fuji TV aired footage in June 2006 of a man it said was Jong-chol in Berlin and said he had attended Eric Clapton concerts in four cities with a young woman believed to be his girlfriend.  Jong-chol is also said to play the guitar and has performed with his own band in front of his father.