"I want to thank China for giving early warning on the test. We understand that North Korea informed China 20 minutes ahead of the test. China immediately informed the United States. A lot of people in the United States appreciate that," Kirk said in an interview with Xinhua.

Kirk also commended China's "very positive" role in trying to resolve the DPRK nuclear issue. "The Chinese government was very clear against upsetting the balance in Asia and Chinese government's position after the test was very encouraging," he said.

After the DPRK claimed that it had conducted a nuclear test, the Chinese Foreign Ministry issued a statement saying that the Chinese government is "resolutely" opposed to the nuclear test and demands the DPRK to live up to its commitment to denuclearization on the Korean Peninsula.

"I think that means China is right in the line with all the other major powers in Asia," Kirk said, adding that both the United States and China are working very closely together and "the statements they made in public are very similar."

As the DPRK nuclear test might start an arms race in Asia, Kirk said the Bush administration will ask China to restrict trade with the DPRK and cooperate on making sure that the DPRK can not ship any nuclear weapons to other countries. "China has a key role to play in the crisis," he said.

"The United States and China are key players in resolving the crisis, and if the United States and China speak with one voice, we have a very strong opportunity to resolve this," Kirk said.

As to the U.S. Congress, Kirk said when it returns to session in mid-November, it will call for "very strong" actions against the DPRK, including sanctions and searching all DPRK ships to make sure nuclear weapons are not leaving the country.

Earlier Monday, U.S. President George W. Bush said the United States condemns the claimed nuclear test and demands immediate UN Security Council action.

"Such a claim itself constitutes a threat to international peace and security. The United States condemns this provocative act," Bush said in a statement.

Bush said he has held conversations with leaders of China, South Korea, Russia and Japan. "We reaffirm our commitment to a nuclear-free Korea peninsula, and all of us agree that the proclaimed actions taken by North Korea are unacceptable and deserve an immediate response by the United Nations Security Council," Bush said.

The DPRK claimed Sunday night that it had successfully set off its first nuclear test.

The nuclear test came about a week after the country announced it would undertake an unprecedented nuclear test under the condition where safety is firmly guaranteed.

According to a report by the official Korean Central News Agency, there was no such danger as radioactive emission in the test as it was carried out under "a scientific consideration and with careful calculation."