United Nations ? The North Korean nuclear crisis settled into diplomatic debate Tuesday, with China agreeing to punishment but not the severe U.S.-backed sanctions that it said would be too crushing for its impoverished communist ally.

Scientists and other governments, meanwhile, suggested that Monday’s underground test was a partial failure, producing a smaller blast than planned.

In Japan, which is jittery about a second test, media reported that the government had detected tremors in North Korea, leading it to suspect Pyongyang had conducted another detonation.

Officials quickly focused on a strong earthquake as the possible culprit.

“Japanese officials are now saying that this occurrence may be related to an earthquake in northern Japan,” White House spokesman Blair Jones said in Washington.

Japanese Prime Minister Shinzo Abe said he had no information to confirm North Korea had conducted a second nuclear test.

The Bush administration asked the U.N. Security Council to impose a partial trade embargo, including strict limits on Korea’s profitable weapons exports and freezing of related financial assets. All imports also would be inspected, to filter out materials that could be made into nuclear, chemical or biological weapons.

A North Korean official said today that Pyongyang would regard sanctions in response to its claimed nuclear test as tantamount to a declaration of war.

A ship loaded with North Koreans lists as it cruises on the Yalu River in front of the Chinese border city of Dandong. China, North Korea's main source of food and fuel aid, said Tuesday that the North's nuclear test would negatively affect ties between the countries.

The North already is under limited sanctions by the United States and some allies. The U.N. Security Council is considering broader measures in response to North Korea’s claimed nuclear test Monday.

“Sanctions are nonsense. If full-scale sanctions take place, we will regard it as a declaration of war,” the Beijing-based official, who wasn’t identified, told Yonhap.

The statement is a reiteration of the North’s long-held stance on sanctions.

The official said he doesn’t know if North Korea is preparing a second nuclear test, but the North will decide whether to carry out another test “according to the development of the situation.”

The United States reiterated that it would not talk with the North Koreans one-on-one, but Secretary of State Condoleezza Rice assured the North that the U.S. would not attack.

Rice rejected a suggestion that Pyongyang may think it needs nuclear weapons to stave off an Iraq-style U.S. invasion. President Bush, she told CNN, has told “the North Koreans that there is no intention to invade or attack them. So they have that guarantee. : I don’t know what more they want.”

U.S. Ambassador John Bolton sounded upbeat after Tuesday’s round of talks at the Security Council, but said differences remained in advance of today’s meeting.

“Look, we don’t have complete agreement on this yet, that’s hardly a news flash, but we’re making progress and we’re I think at a point we can try and narrow some of the differences we do have,” Bolton said.

Seeking some limits

China, which reacted to Monday’s blast with a strong condemnation but considers North Korea a useful buffer against U.S. forces stationed in South Korea, said it envisioned only a limited package of sanctions – not what the United States and especially Japan were demanding.

China and Russia object to plans to interdict shipments and block financial transactions. They also oppose a new suggestion that Japan proposed Tuesday – to include mention of the North’s abduction of Japanese citizens in the 1970s and ’80s.

“We certainly understand that Japan is close to the country. But I think you cannot ask by this resolution to kill a country,” China’s U.N. Ambassador Wang Guangya said. He said the Security Council must impose “punitive actions” but that they have to “be appropriate.”

Though far less than what the Americans and Japanese seek, even calling for some punishment was significant for China, which usually opposes sanctions, particularly against an ally such as North Korea.

Pyongyang again demanded one-on-one talks with Washington and threatened to launch a nuclear-tipped missile if the U.S. doesn’t help resolve the standoff. Bolton dismissed the demand, saying the North should instead “buy a ticket to Beijing” and rejoin stalled six-nation talks on its nuclear and missile programs.

Small-scale blast

The war of words suggested tough negotiations before the U.N. takes any action against North Korea. In the meantime, scientists and governments tried to determine what exactly happened early Monday, deep below the earth in North Korea’s northeast mountains. The North Korean government has released few details.

A South Korean newspaper quoted a North Korean diplomat, whom it did not name, saying that the blast was “smaller in scale than expected.

“But the success in a small-scale (test) means a large-scale (test) is also possible,” he said in comments posted on the Web site of the liberal newspaper Hankyoreh, which has good ties with the communist nation.

The diplomat also said the North could take “additional measures” and that it doesn’t fear sanctions.

Philip Coyle, at the Center for Defense Information in Washington, D.C., a nongovernment think tank, expressed a growing view that “they got a partial result” and not the full-power explosion that they sought. Several Western estimates said the blast was less than a tenth the size of the bomb that the United States dropped on Hiroshima in 1945; the force of the Hiroshima bomb was equivalent to 15,000 tons of TNT.

But “for them it was enough … to say that it was a success. It helps them to claim that they are a nuclear power, and that the world should take them seriously, which is what they want. But I wouldn’t be surprised if after several months they don’t try again.”

The White House said there is a “remote possibility” that the world never will be able to fully determine whether North Korea succeeded in conducting a nuclear test Monday.