SEOUL, South Korea — North Korea appears to be preparing to test an advanced missile designed to reach the United States, a U.S. official said Monday, ratcheting up tensions after its second nuclear blast. Media reports say the North Korean leader's youngest son has been picked to be the next leader.
The reclusive communist country also reportedly bolstered its defenses and conducted amphibious assault exercises along its western shore, near disputed waters where deadly naval clashes with the South have occurred in the past decade.
Satellite images and other intelligence indicated the North had transported its most advanced long-range missile to the new Dongchang-ni facility near China and could be ready to be fired in the next week or so, South Korea's Yonhap news agency reported.
A U.S. official confirmed the Yonhap report and said the missile was moved by train, although he did not comment on where it was moved to, and said it could be more than a week before Pyongyang was ready to launch. He spoke on condition of anonymity because the issue involved intelligence.
On Tuesday, Seoul's Chosun Ilbo newspaper reported that the North could have manufactured up to four long-range missiles through the end of last year. That means the regime could fire more missiles after the one being readied for a launch.
The paper cited an unidentified South Korean government official.
Also on Tuesday, South Korean media reported that North Korean leader Kim Jong Il's youngest son, Jong Un, has been picked to be the reclusive nation's next leader. The decision came after the nuclear test and North Korean diplomats have been instructed to respect the decision, the Hankook Ilbo and Dong-a Ilbo reported.
Little is known about the 26-year-old man. He studied at the International School of Berne in Switzerland until 1998, learning to speak English, German and French, the Swiss weekly news magazine L'Hebdo reported in March, citing classmates and school officials.
The reports about the possible leadership succession come amid growing tensions stoked by the nuclear and missile tests.
The latest activity at the launch site came as the United Nations Security Council mulled punitive action for North Korea's May 25 nuclear test, and ahead of a June 16 summit in Washington between South Korean President Lee Myung-bak and President Barack Obama.
U.S. Ambassador Susan Rice reported Monday that key powers are making progress on a new U.N. resolution that will almost certainly expand sanctions against North Korea for conducting a second nuclear test in defiance of the Security Council.
Complicating the situation further, a trial was set to begin Thursday in Pyongyang of two American journalists, Laura Ling and Euna Lee, accused of entering the country illegally and engaging in "hostile acts."
The missile being prepared for launch was believed to be an intercontinental ballistic missile with a range of up to 4,000 miles (6,500 kilometers), the JoongAng Ilbo newspaper reported, citing an unnamed South Korean official.
That distance would put Alaska and U.S. bases on the Pacific island of Guam _ along with all of Japan _ within striking range.
Even so, U.S. Defense Secretary Robert Gates, visiting Manila in the Philippines, said that although North Korea does appear to be working on its long range missiles, it was not yet clear what its plans were for them.
President Lee, hosting a conference of Southeast Asian leaders on the southern island of Jeju, warned in his weekly radio address that the South would "never tolerate" military threats.
Lee Sang-hyun, director of the Security Studies Program at the Sejong Institute in Seoul, said the North's moves were calculated to get international attention.
"North Korea wants to become a full nuclear state, then negotiate," he said. "As a nuclear state, it will have more to gain from the U.S."
Tensions meanwhile increased off the Koreas' western coast.
South Korean coast guard ships were escorting fishing boats near the island of Yeonpyeong, and Yonhap reported that North Korean troops conducted amphibious assault maneuvers along with training on speedboats that could be preparations for skirmishes at sea.
The Koreas ended their three-year war in 1953 with a truce, but North Korea said last week it would no longer abide by the conditions of the armistice. It also disputes the U.N.-drawn western sea border, around which deadly clashes with South Korea occurred in 1999 and 2002.
No incidents have been reported in the Demilitarized Zone that separates the two Koreas, and life seemed normal on the North Korean side of the Yalu River, which marks the country's border with China.
A group of women soldiers patrolled the banks with rifles on their backs, while their male counterparts bathed in the river, using little red plastic buckets to dump waters on themselves. Dock workers unloaded big bundles of goods, while nearby a couple posed for wedding photos, the bride wearing a long traditional Korean hanbok dress.
North Korea's media have defended the country's defiant stance, saying it had been provoked by South Korea and the United States. It said the number of spy planes operating in its airspace had risen dramatically.
Experts said North Korea's nuclear capabilities, while improving, still do not pose a direct threat to its neighbors. The larger concern, they say, is that the North will try to sell its technology to others.
Lee of the Sejong Institute said the international community's options were few.
"If North Korea is determined to become a full nuclear state, there's nothing the international community can do about it," he said.
Associated Press writers Siyoung Lee and Young-joon Ahn on Yeonpyeong island, Ng Han Guan in Dandong, China, William Foreman in Seoul, Lara Jakes in Manila, Philippines, Pauline Jelinek in Washington DC and Edith Lederer at the United Nations contributed to this report.