Secretary of State Condoleezza Rice is launching an uncertain diplomatic drive to persuade Asian allies and Russia to intensify North Korea's isolation by enforcing U.N. curbs on trade in dangerous goods.

Rice was scheduled to leave Tuesday for Japan, the first stop on a four-nation trip, amid clear signs of unease in China and South Korea about even the softened sanctions approved last week by the U.N. Security Council. The U.N. resolution was aimed at forcing North Korea to drop its nuclear weapons program.

The White House said Tuesday that it wouldn't be surprising if North Korea were to try another nuclear test "to be provocative."

"It would not be a good thing for them, but it certainly would not be out of character," said White House press secretary Tony Snow. "We're not going to discuss any particular matters of intelligence, but if you take a look at the record, I think it is reasonable to expect that the government of North Korea will do what it can to test the will, the determination and the unity of the United Nations."

Asked why it would not be a good thing for North Korea, Snow said, "If they do believe that somehow people are going to give them a pass on this, they're going to find out that they're wrong."

Rice sought at a news conference on Monday to brace anxious capitals with reassurances that the United States "has both the will and capacity to meet the full range of our security commitments to allies like South Korea and Japan."

She said she intended to reaffirm "our reciprocal obligations" on her trip but also said "every country in the region must share the burdens as well as the benefits of our common security." She also plans to visit South Korea, China and Russia.

The resolution was approved unanimously by the Council only after the United States, the chief sponsor, accepted limitations on inspections of cargo and agreed that only material linked with unconventional and advanced weapons would be denied to the insular Communist regime, which reported detonating a nuclear device Oct. 9.

On Monday, National Intelligence Director John Negroponte's office released the first definitive U.S. confirmation that North Korea tested a nuclear device last week.

The statement said the explosion was smaller than a kiloton, the force produced by 1,000 tons of TNT, smaller than many experts had expected.

One intelligence official said the North Korean device was believed to be roughly equivalent to 200 tons of TNT, suggesting it was probably a partial failure. The official spoke on condition of anonymity because of the sensitive situation with Pyongyang.

U.S. intelligence has concluded that the North Korean device likely used plutonium, as opposed to uranium.

South Korea, technically in a state of war with North Korea since the 1950-53 Korean conflict ended in a cease-fire, is jittery about confronting Pyongyang, while China and Russia have preferred more diplomacy to sanctions.

China, which has been at the center of efforts to reverse North Korea's nuclear weapons and missiles programs, has said it would not stop and inspect cross-border shipments.

On Monday, Chinese customs officials inspected trucks at the North Korean border, but China's U.N. ambassador, Wang Guangya, indicated Chinese inspectors would not board ships to look over equipment for weapons programs.

"I am not concerned that the Chinese are going to turn their backs on their obligations," Rice said at her State Department news conference. "I don't think they would have voted for a resolution that they did not intend to carry through on."

South Korea, Japan, Russia and "the rest of the international system" consider North Korea's nuclear program unacceptable, Rice said.

She sent Christopher Hill, the top U.S. nuclear negotiator, to Japan ahead of her arrival, and directed him to go on to South Korea as well.

Japan, more hawkish than most other countries on challenging North Korea, issued a positive statement after Hill's talks in Tokyo.

"We agreed to cooperate with other countries to swiftly implement" sanctions to get the North to abandon its nuclear weapons program, senior Japanese negotiator Kenichiro Sasae said.

Mindful of widespread reluctance to take a tough stand against the unpredictable North Korean regime, Rice at times took a conciliatory approach in her remarks Monday.

"If North Korea reverses course and embraces the path of cooperation, if it makes the strategic choice to dismantle its nuclear weapons completely, briefly and irreversibly, an entirely new and better future would be open to it and to its people," she said.

Rice said she was aware that some countries wished to be certain that the sanctions "won't ratchet up conflict."

"We have no desire to ratchet up conflict, either," she said.

Meanwhile, North Korea has given no public indication it will be influenced by the U.N. sanctions. It has accused the Security Council of gangsterism and warned that any American pressure on the North Korean government would be regarded as an act of war.

Secretary of State Condoleezza Rice launched an uncertain diplomatic drive Tuesday to persuade Asian allies and Russia to intensify North Korea's isolation, even as the White House acknowledged that the reclusive nation might try a second nuclear test.

Rice left for Japan, the first stop on a four-nation trip, amid clear signs of unease in China and South Korea about even the softened sanctions approved last weekend by the U.N. Security Council. The U.N. resolution was aimed at forcing North Korea to drop its nuclear weapons program.

Concern over a second test stems partly from new satellite imagery showing increased activity around at least two other North Korean sites, a senior defense official said Tuesday.

The activity, started a number of days ago, included ground preparation at one site and construction of some buildings and other structures, said the official, who spoke on condition of anonymity because it involved intelligence gathering. He said that although the purpose of the structures is unclear, officials are concerned because North Korea has left open the possibility of another test.

The White House said Tuesday that it wouldn't be surprising if North Korea were to try another nuclear test "to be provocative."

"It would not be a good thing for them, but it certainly would not be out of character," said White House press secretary Tony Snow. "We're not going to discuss any particular matters of intelligence, but if you take a look at the record, I think it is reasonable to expect that the government of North Korea will do what it can to test the will, the determination and the unity of the United Nations."

Asked why it would not be a good thing for North Korea, Snow said, "If they do believe that somehow people are going to give them a pass on this, they're going to find out that they're wrong."

Rice sought at a news conference on Monday to brace anxious capitals with reassurances that the United States "has both the will and capacity to meet the full range of our security commitments to allies like South Korea and Japan."

She said she intended to reaffirm "our reciprocal obligations" on her trip but also said "every country in the region must share the burdens as well as the benefits of our common security." She also plans to visit South Korea, China and Russia.

The resolution was approved unanimously by the Council only after the United States, the chief sponsor, accepted limitations on inspections of cargo and agreed that only material linked with unconventional and advanced weapons would be denied to the insular Communist regime, which reported detonating a nuclear device Oct. 9.

On Monday, National Intelligence Director John Negroponte's office released the first definitive U.S. confirmation that North Korea tested a nuclear device last week.

The statement said the explosion was smaller than a kiloton, the force produced by 1,000 tons of TNT, smaller than many experts had expected.

One intelligence official said the North Korean device was believed to be roughly equivalent to 200 tons of TNT, suggesting it was probably a partial failure. The official spoke on condition of anonymity because of the sensitive situation with Pyongyang.

U.S. intelligence has concluded that the North Korean device likely used plutonium, as opposed to uranium.

South Korea, technically in a state of war with North Korea since the 1950-53 Korean conflict ended in a cease-fire, is jittery about confronting Pyongyang, while China and Russia have preferred more diplomacy to sanctions.

China, which has been at the center of efforts to reverse North Korea's nuclear weapons and missiles programs, has said it would not stop and inspect cross-border shipments.

On Monday, Chinese customs officials inspected trucks at the North Korean border, but China's U.N. ambassador, Wang Guangya, indicated Chinese inspectors would not board ships to look over equipment for weapons programs.

"I am not concerned that the Chinese are going to turn their backs on their obligations," Rice said at her State Department news conference. "I don't think they would have voted for a resolution that they did not intend to carry through on."

South Korea, Japan, Russia and "the rest of the international system" consider North Korea's nuclear program unacceptable, Rice said.

She sent Christopher Hill, the top U.S. nuclear negotiator, to Japan ahead of her arrival, and directed him to go on to South Korea as well.