North Korea is readying an advanced missile designed to reach the United States for a launch that could come within weeks, reports said Monday, ratcheting up tensions after its second underground nuclear test.
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.
The 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.
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 recent actions do not come completely without warning.
In late April, the North threatened to conduct nuclear and long-range missile tests unless the Security Council apologized for criticizing an April 5 launch that it claims put a satellite into orbit.
Last week, it threatened to take further "self-defense" measures if the Security Council provokes it. That threat was seen as referring to an ICBM test.
Underscoring the threat, the North has designated a large area off its west coast as a "no-sail" zone through the end of next month, the Chosun Ilbo newspaper said, citing unidentified intelligence officials.
North Korea's media 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.
"The U.S. imperialists and the South Korean puppets perpetrated at least 200 cases of aerial espionage against the DPRK in May, or 30 cases more than those in the same month of last year," it said in a report in its official Korean Central News Agency.
The DPRK is an acronym for North Korea's official name, the Democratic People's Republic of Korea.
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.