Aides to the youngest son and heir apparent of North Korean leader Kim Jong-Il planned an attack last year on Kim's oldest son but were warned off by China, a report said Wednesday.

South Korea's Chosun Ilbo newspaper, citing a government source, said close aides of youngest son Jong-Un plotted an attack on Jong-Nam after the leader had picked Jong-Un as heir apparent in January 2009.

Jong-Nam has been living mainly in Beijing and the Chinese territory of Macau since falling out of favour with his father.

In an frank interview with Japan's TV Asahi broadcast Tuesday, he expressed opposition to another hereditary power transfer in the communist state.

Chosun quoted its source as saying Jong-Un's aides last year tried "to do something to Kim Jong-Nam, who has a loose tongue abroad" but China apparently warned them not to lay a hand on him on Chinese soil.

The paper said Jong-Nam reportedly has close ties with China's powerful "princelings", an elite group of the children of senior officials.

"Kim Jong-Nam won't go back to the North but stay in China," the source added.

South Korea's intelligence agency declined comment on the newspaper report.

Jong-Un's status as leader-in-waiting was effectively made public after Pyongyang made him a four-star general and gave him key ruling party posts late last month.

He appeared Sunday with his father at a massive military parade seen as a coming-out party.

Jong-Nam fell out of favour when he was caught trying to enter Japan with a fake passport in 2001.

China is the impoverished North's sole major ally and economic lifeline, its biggest trade partner and energy supplier.

"Personally I am opposed to the hereditary transfer to a third generation of the family," Jong-Nam told TV Asahi in the interview conducted in Beijing on Saturday.

Leader Kim Jong-Il succeeded his own father Kim Il-Sung, who died in 1994.

However, the 39-year-old Jong-Nam also said he would accept his father's choice and that "for my part, I am prepared to help my younger brother whenever necessary while I stay abroad".

A North Korea expert at Seoul's Dongguk University, Kim Yong-Hyun, said Jong-Nam's comments appeared to be a signal from the regime.

"His interview is seen as a message to the outside world that there is no internal friction over the transfer of power," the professor told AFP.

"Jong-Nam is also saying he will continue to stay abroad. The interview indicates there is no room for him to play in North Korea's current power structure."