N. Korea Claims Nuclear Test

The U.S. government planned to make a statement condemning the test and calling an emergency meeting of the U.N. Security Council, officials said. U.S. officials are considering a number of other actions to take against Pyongyang, which could also include new economic measures.

Japan, which considers itself the most vulnerable to a North Korean attack, agreed with U.S. officials to immediately call for an emergency meeting of the U.N. Security Council to seek a tough, binding resolution that would force North Koreans back to stalled six-nation talks aimed at dismantling its nuclear weapons programs.

The Security Council has repeatedly warned North Korea to desist from provocative actions, and to resume multiparty talks over the future of its nuclear program. On Friday, the 15-nation council issued a statement expressing "deep concern" about Pyongyang's pledge to conduct its first test of a nuclear explosive, saying it would "jeopardize peace, stability and security in the region and beyond."

The council issued a veiled threat to consider tough action, including the possibility of sanctions, against Pyongyang if it conducted a test, warning that a nuclear test "would bring universal condemnation."

The test dramatically complicates the stalled attempts to force Kim's secretive government to give up its nuclear weapons programs. In late 2002, North Korea took a series of steps including kicking out international weapons inspectors and reprocessing plutonium in defiance of the international community.

The Bush administration rebuffed North Korea's calls for bilateral talks to solve the crisis, instead pushing for an international framework that forced the North to the bargaining table with the United States, but also China, Japan, Russia and South Korea.

Monday's test, analysts said, provided unmistakable evidence that the six-party framework had failed, leaving Washington and its partners in the region now facing the profoundly more difficult task of disarming a state that has already fulfilled its nuclear ambitions. No nation that has successfully conducted a nuclear test has ever been persuaded to give up the weapons through diplomacy, sanctions or other means.

To be sure, U.S. and Asian intelligence officials have estimated that the North could possess nuclear material for as many as a dozen nuclear weapons -- and last February, North Korea unilaterally declared itself a nuclear power. But until today, there was no proof to those claims.

Given North Korea's million-man army and vast array of ballistic missiles, which could easily reach huge population centers such as Tokyo and Seoul, U.S. officials have largely discounted any military solution. Instead, the Bush administration is likely to push for tougher economic sanctions at the United Nations.

Japan, which has already imposed limited economic sanctions on North Korea, has additionally said it will take a host of harsher measures. But few analysts believe Washington and Tokyo's efforts alone would serve to successfully pressure North Korea back to the negotiations.

Instead, analysts pointed to the still unclear responses from China and South Korea, the impoverished North's two largest benefactors who have kept Kim's government afloat through billions of dollars in trade and aid out of fear that a messy collapse his government could generate an economic disaster of refugees flooding over their borders. South Korea has been unclear about what impact a test would have on its detente with the North, which has including the construction of tourism resorts and a vast industrial park on the other side of the border. But analysts were mostly watching reaching from China, which has the power to cut off flows of oil into North Korea.

U.S. officials had particularly put stock in China's ability to control the North Koreans, faith that analysts now say appears to have been ill placed. The Chinese, publicly and unambiguously, did warn the North Korea's against testing since they announced their attention to do so last Tuesday. But the North, long thought be under China's sphere of influence, seems to have dismissed Beijing's orders.

"The North Koreans are making a statement that 'you guys can gang up on us. but you can't change us,' " said Lho Kyong Soo, international relations professor at Seoul National University. "Now, they're hoping they could get away with this like Pakistan. They're saying treat us with respect and accept us this way because we are not going to change."

James A. Kelly, a former U.S. assistant secretary for East Asian and Pacific Affairs who previously handled the Bush administration's dealings with North Korea, said last week that Pyongyang's timing may have been prompted in part by the imminent selection of Ban as U.N. Secretary General. The North has smarted in the past at having to deal with the South Koreans, rather than directly with the Americans, in any type of diplomatic conflict.

"It's possible this threat of the tests is as much aimed at Ban Ki Moon as otherwise," Kelly said. "It's a big part of North Korea's obsessions with direct dealings with Americans is to avoid giving direct legitimacy to South Korea."

But U.S. officials said early this morning that the Security Council planned to go ahead with Ban's election as the first order of business before turning to North Korea, in an effort to show that North Korea's action will not deter his selection.

South Korea's intelligence agency said Monday that the test site appears to have been at Musudan-ri, North Hamgyong Province, in warren-like underground tunnels in the mountains not far from where the North Koreans tested 7 ballistic missiles on July 4th.

Although South Korean officials detected an explosion measuring 3.58, the Reuters News Service quoted the U.S. geological survey office as having detecting a 4.2 magnitude tremor, which could mean the tested device was somewhat more powerful than originally thought.

Kessler reported from Washington, Linzer from New York. Special correspondent Joohee Cho in Seoul and staff writers Colum Lynch at the United Nations and Ann Scott Tyson in Washington contributed to this report.