North Korea has told top officials to pledge allegiance to Kim Jong Il's youngest son, apparently setting him up to succeed his 67-year-old father.

A senior U.S. intelligence official confirmed South Korean media reports that the secretive communist state was sending "guidance" to its missions in foreign countries to swear fealty to 26-year-old Kim Jong Un as the next leader of North Korea.

"The directive went out," the official told FOX News. "This guidance isn't a suggestion — it's an order."

The official described the directive as a milestone in the history of North Korea. But the official contradicted a Reuters report that suggested North Korea would ratchet down tensions and enter talks over its nuclear program, having worked out its line of succession.

Rather, U.S. intelligence officials have observed the arrival of the first-stage transporter for a Taepodong-2 intercontinental ballistic missile at a newly constructed launch site on the nation's west coast, FOX News has learned.

"They're getting ready," the intelligence official said, adding: "They're not doing this for show. This takes a lot of money, a lot of manpower. ...The transporter is there. Stuff is moving there."

At the same time, American intelligence officials have observed stepped-up activity at the Kittaeryong complex in on the east coast. U.S. officials have spotted components associated with medium-range Nodong missiles at Kittaeryong.

A senior U.S. defense official with access to the latest intelligence also said Tuesday there is not yet any sign that North Korea is de-escalating the tense military stand-off on the Korean peninsula.

The official said North Korea still appears to be preparing for a long-range ballistic missile launch.

North Korea sent the message about Jong Un, after the nation's May 25 nuclear test, which along with a series of missile tests has greatly raised tensions in the region, the Hankook Ilbo reported.

The paper cited unnamed members of South Korea's parliamentary intelligence committee briefed by the spy agency.

Kim Jong Il's youngest son reportedly enjoys skiing and studied English, German and French at a Swiss school.

Opposition lawmaker Park Jie-won, an intelligence committee member, said during a radio interview Tuesday that he was briefed by the government on the North's move and the regime is "pledging allegiance to Kim Jong Un," according to an interview transcript provided by his office.

Another mass-market paper, Dong-a Ilbo, carried a similar report, saying the North is teaching its people a song lauding the son. The paper cited unidentified sources.

The spy agency, National Intelligence Service, said it cannot confirm the reports.

The possible transfer of power comes at a tense time as the North escalates tensions in the region by testing the nuclear device and several short-range missiles.

The saber-rattling is believed to be part of the North's succession campaign, the papers said.

Most analysts have long believed Kim's youngest son has the best chance of succeeding the authoritarian leader. But little is known about Jong Un, the youngest of three sons Kim Jong Il is known to have fathered.

He studied at the International School of Berne in Switzerland until 1998 under the pseudonym Pak Chol, learning to speak English, German and French, the Swiss weekly news magazine L'Hebdo reported earlier this year, citing classmates and school officials.

A classmate recalled him as timid and introverted but an avid skier and basketball player who was a big fan of the NBA star Michael Jordan. He was humble and friendly with the children of American diplomats, a former school director said. A car arrived every day after school to pick him up, the report said.

A Japanese man who claims to know Jong Un from his years as Kim Jong Il's sushi chef says the son looks and acts just like his father and is the leader's favorite. In contrast, Kim often derided the middle son, Jong Chul, as "girlish," the chef, Kenji Fujimoto, said in a 2003 memoir.

Who will eventually rule the nuclear-armed North has been the focus of intense media speculation since leader Kim, 67, reportedly suffered a stroke last summer. That sparked regional concerns about instability and a possible power struggle if he died without naming a successor.

Kim's eldest son, Jong Nam, 38, had long been considered the favorite to succeed his father — until he was caught trying to enter Japan on a fake passport in 2001. He reportedly told Japanese officials he wanted to visit Tokyo Disneyland.

Kim considers the middle son, Jong Chol, too effeminate for the job, according to the sushi chef's 2003 memoir.

Kim succeeded his father, who died in 1994, in communism's first hereditary power succession. He rules the country with absolute authority and has allowed no opposition.

FOX News' James Rosen and Jennifer Griffin and The Associated Press contributed to this report.