Kim Jong Un, the youngest son of North Korean leader Kim Jong-il, secretly visited China last week and met with President Hu Jintao, Japan's Asahi newspaper reported on Tuesday.

The 26-year old scion reportedly flew to Beijing around June 10, accompanied by senior officials, including his aide.

The aide used the occasion to inform Chinese officials that Jong Un had been appointed as the leader's successor, the Asahi newspaper said.

The Chinese leader urged him to have North Korea refrain from carrying out further nuclear and missile tests, said the newspaper, quoting unnamed North Korean sources in Beijing.

The report also said that Jong Un asked China to continue its energy and food aid to North Korea.

Earlier this month South Korean media, quoting informed sources, said Pyongyang had asked the country's main bodies and overseas missions to pledge loyalty to him, indicating he will take over from his father.

If what was said in the paper is proven to be true, it would not be a stretch to say the decision to make him heir is official, said Ko Yu-hwan, a professor of North Korean studies at Seoul's Dongguk University.

Chinese Foreign Ministry spokesman said he had no knowledge of the reported visit.

On the North Korean side, state media has never told its public that leader Kim has offspring, let alone report on the journey of a son to China.

Jong Un is the Swiss-educated third son of Kim Jong-il and was born in 1983 or 1984. He studied at the International School of Berne in Switzerland until 1998 under a pseudonym and learned English, German and French, the Swiss weekly news magazine L'Hebdo reported earlier this year.

Leader Jong Il, 67-year-old, is believed to have suffered a stroke last year.

Analysts have said North Korea's nuclear test on May 25 and other belligerent acts may be aimed at a domestic audience, with the elder Kim trying to bolster his position at home to secure the succession of his youngest son.