By Kazunori Takada

Tokyo - Japan is detaining the eldest son and heir-apparent of North Korean leader Kim Jong-il after he was caught trying to enter the country on a fake passport to take a four-year-old to Disneyland, said Kyodo news agency on Thursday.

It said Kim Jong-nam, 29, had acknowledged his identity to Japanese authorities and told them he tried to enter the country because he wanted to visit Disneyland.

"I am Kim Jong-nam," Kyodo quoted the man as telling police investigators.

The agency said Kim, being groomed by Kim Jong-il to inherit the world's first communist dynasty, had previously entered Japan twice on the fake passport.

"I wanted to go to Disneyland," Kyodo quoted him as saying. He arrived on Tuesday aboard a Japan Airlines flight from Singapore and was found to be carrying a fake passport from the Caribbean nation of the Dominican Republic.

Kim studied Japanese in Japan when he was younger and has been described as an Internet aficionado, but his high profile now makes it hard for him to move about freely, said Koh Yu-hwan, an expert on North Korea at South Korea's Dongguk University.

"He is believed to have travelled to other countries and his position makes it difficult to travel under his real identity," said Koh.

Although the younger Kim is not believed to want to stay in Japan, the incident poses an early diplomatic test for new Prime Minister Junichiro Koizumi.

North Korea, designated by the United States as a "state that sponsors terrorism", has long had fraught relations with Japan, its former colonial power.

Talks aimed at normalising relations have been stalled for more than six months.

Koizumi held an emergency meeting with deputy foreign minister Yutaka Kawashima to discuss the matter, but government officials were cagey.

"We can neither confirm nor deny such reports. We are not supposed to comment on matters that involve someone's privacy," said a justice ministry spokesperson.

The man is being held together with three travelling companions, two women in their 30s and a four-year-old boy, at the East Japan Immigration Control Detention Centre in Ibaraki Prefecture, north-east of Tokyo.

All were believed to be members of his family.

Eager to be rid of a potential diplomatic crisis, Japanese officials were considering deporting Kim to China, said Kyodo.

But the Jiji news agency said he might be sent back to Singapore, where his flight to Tokyo originated.

Police took Kim into custody at Narita airport east of Tokyo after he arrived at 3pm on Tuesday aboard a Japan Airlines flight from Singapore and was found to be carrying a fake passport in the name of Pang Xiong, said Kyodo.

It also reported that the group had return tickets to leave on May 7 for Beijing.

Kim Jong-il, who was holding talks on Thursday in Pyongyang with a high-level European Union delegation, is believed to be grooming Kim Jong-nam to take over the reclusive state.

Koh, the South Korean expert, described Kim as the strongest candidate to succeed his father, who himself took over the reins of power when his own father died in 1994.

Kim Jong-nam accompanied his father to China in January, where he was believed to have witnessed how his country's biggest ally opened its economy to the outside world, said Koh.

"He is known to be very interested in the Internet and hi-tech industry, as well as the latest trends in advanced countries," he added.

The Chinese magazine Guang Jiao Jing also says Kim Jong-il plans to designate Kim Jong-nam as his successor.

It said the junior Kim is known in the North as "Little General".

Details of the family of the secretive North Korean leader are murky but Kim Jong-nam is understood to have studied in Moscow and Geneva.

He is reported to hold an important position in the North's People's Army and is described in media reports as being slightly overweight and bespectacled, like his enigmatic father.

Kim Jong-nam's mother is believed to be the former actress Sung Hye-rim, although she and Kim Jong-il are never thought to have married and separated many years ago. - Reuters