The eldest son of North Korean leader Kim Jong-Il has returned home after spending years abroad in a move that could be linked to the ruler's plans to choose an heir, a man close to Kim's son said Monday.

Kim Jong Nam, 36, traveled from China to Pyongyang in late June, and his return "has decisive relations to the power transfer," the man told The Associated Press by telephone from the U.S. He spoke on condition of anonymity, citing the sensitivity of the issue.

South Korea's top spy agency, the National Intelligence Service, declined to confirm the son's return.

Kim Jong Il has not publicly named an heir yet, prompting speculation abroad about who might eventually take the reclusive country's helm — and whether Kim will designate one of his sons as the next leader, continuing the world's only communist dynasty.

Kim took over the leadership of North Korea following the death in 1994 of his father, national founder Kim Il Sung.

The South's spy agency had said in a report earlier this year that another father-to-son succession appears highly likely in the North. However, it indicated that there is also the possibility of a collective leadership in case of Kim Jong Il's sudden death.

The elder Kim is said to be suffering from heart disease and diabetes, but the National Intelligence Service also has said his health is not believed to be as bad as some media reported in recent months. The agency said there was no sign that chronic diseases are affecting his public activities.

The junior Kim "has played a key role in North Korea," and his return means "he will proceed to the next step" in plans outlined for him, said the man in the U.S., who said he has developed a close business relationship with the leader's son and has been in contact with him.

Those plans involve South Korea's aid to the North, the North's relations with the U.S. and the replacement of a cease-fire that ended the 1950-53 Korean War with a peace treaty, the man said, without giving further details.

The junior Kim has long been believed to have fallen out of favor after embarrassing his father in 2001, when he was caught trying to enter Japan on a fake passport, saying he wanted to visit Tokyo Disneyland.

But the man said the allegation was made by South Korea to discredit the junior Kim as a possible successor.

Kim Jong Nam was born to Kim Jong Il from an unofficial relationship with North Korean actress Sung Hae Rim, who died in Moscow in 2002.

The son is widely believed to have lived in China and its territory of Macau for the past several years.

The elder Kim is known to have two other sons — Kim Jong Chol and Kim Jong Un — with his second wife, Ko Yong Hi, who died in 2004.

Some North Korean experts say middle son Kim Jong Chol, 26, is most likely to become the North's next leader. Little is known about him except that he studied in Switzerland and is a fan of U.S. professional basketball.