North Korean leader Kim Jong-il has reportedly selected his third and youngest known son to succeed him.
Mr Kim is thought to be recovering from serious illness and sightings of him in public have not been confirmed for some time.
The demise of the 66-year-old without a clear successor could likely add to the uncertainty of a country trying to develop nuclear weapons but with an economy in ruins and a population constantly on the edge of famine.
The question of succession in the secretive communist state is so closely guarded that no-one outside Mr Kim's immediate circle of family and confidants is thought to have any clear knowledge of the situation.
But speculation about his health and the succession is a favourite topic in South Korea.
'We believe Chairman Kim Jong-il has picked the son Jong-un he had with third and late wife Ko Yong-hui and given instructions to the Workers' Party Organisation and Guidance Department around 9 January,' Yonhap news agency reported, quoting an anonymous source.
Senior officials of the powerful party apparatus, where Kim Jong-il himself began his training as anointed leader before succeeding his father in 1994, have been instructed to pass the message down the ranks, the source was quoted as saying.
South Korea's spy agency said despite various reports over the question of succession in North Korea, nothing has been confirmed.
Swiss-educated Kim Jong-un is believed to have been born in late 1983 or early 1984 and has been described as his father's favourite and an intelligent and thoughtful man.
But his youth has often been cited as a barrier to his rise to power in a society where the tradition of seniority is strong.
South Korean media has portrayed eldest son Jong-nam - in his late 30s and seen in file footage as overweight and unkempt - as out of favour.
They say the second, Jong-chol, is considered by his father as too weak to take over power.
Former South Korean President Kim Dae-jung, who held the first summit meeting with the North's leader in 2000, said this morning that one of the three sons is likely to be installed as symbolic leader, with a cabinet of officials from the military and the party forming a collective leadership.
