TOKYO - The youngest son of North Korean leader Kim Jong-il secretly visited ally China around last week as a special envoy of his father and met with Chinese President Hu Jintao, Japan's Asahi newspaper reported on Tuesday.

The report, which cites unidentified sources close to North Korea, comes days after the U.N. Security Council approved a resolution banning all weapons exports from the hermit state, which raised regional tension by conducting a nuclear test in May.

Analysts have said the North's belligerence may be aimed largely at a domestic audience, with the 67-year-old leader, believed to have suffered a stroke last year, using it to bolster his position at home to better secure the succession of his youngest son, Kim Jong-un.

Jong-un, the Swiss-educated third son of Jong-il and born in 1983 or 1984, flew to Beijing around June 10 and met with Hu and other heavyweights of the Chinese Communist Party, the Asahi reported.

China is a neighbor and the biggest trade partner of North Korea and is the closest Pyongyang has to a major ally.

An aide to Jong-un told the Chinese side he had already been appointed heir to the ruling family dynasty and he holds an important post in the ruling Korean Workers' Party, the Asahi reported.

Jong-un is believed to have asked China for emergency energy and food aid, while Hu seems to have asked North Korea to stop its apparent plan to conduct a third nuclear test as well as to test-fire an intercontinental ballistic missile, the Asahi reported.

North Korea has threatened to boost its nuclear program and has raised regional tensions in recent months by test-firing missiles and restarting a plant to produce arms grade plutonium. It conducted a nuclear test on May 25.

Jong-un also visited factories in Guangdong province, it said.

The succession has been one of the most closely guarded secrets in North Korea, and very little is known about Jong-un, whose youth is seen as a possible problem in a society that attaches importance to seniority.

(Reporting by Yoko Kubota; Editing by Michael Watson)