President Bush has condemned North Korea's claim that it carried out a successful nuclear test as a "provocative act" that threatens international peace and security.
Signalling a more confrontational approach to Pyongyang, Washington called for a United Nations Security Council resolution to impose sanctions on North Korea under Chapter Seven of the UN Charter, which can authorise the use of military force.
The security council took just 30 minutes to issue a unanimous condemnation of North Korea's action and officials started work yesterday evening on drafting a new resolution. US ambassador John Bolton said he was impressed by the unity of purpose among the 15 security council member-states and expressed confidence that they would agree on tough action against Pyongyang.
"We're looking for very swift action by the security council. We think it's important to respond even to the claim of a nuclear test by the North Koreans and we'll be going 24/7 if we need to be to get this resolution adopted quickly," he said.
Britain and France immediately backed Mr Bolton's call for a Chapter Seven resolution but Russian ambassador Vitaly Churkin struck a more cautious note and made no mention of sanctions.
"We condemn the test. We demand that they return to the regime on non-proliferation and to the six-party talks. I think the North Koreans will be facing a very serious attitude on the part of the security council and the entire international community," he said.
Mr Bush said he spoke by phone to the leaders of China, South Korea, Japan and Russia - the other parties involved in stalled, six-party talks with North Korea on its nuclear programme. "We reaffirmed our commitment to a nuclear-free Korean peninsula, and all of us agreed that the proclaimed actions taken by North Korea are unacceptable and deserve an immediate response by the United Nations Security Council," he said. The president warned Pyongyang that any transfer of nuclear weapons or materials "to states or non-state entities" would be viewed as a grave threat to US interests and he affirmed Washington's commitment to protecting Japan and South Korea.
"The United States remains committed to diplomacy, and we will continue to protect ourselves and our interests. I reaffirmed to our allies in the region, including South Korea and Japan, that the United States will meet the full range of our deterrent and security commitments," he said.
North Korea's action has raised questions in Washington about the Bush administration's nuclear non-proliferation policy and is likely to strengthen hardliners who want a tougher approach. Since Mr Bush took office, Pyongyang has restarted a nuclear reactor programme that was frozen since 1994 under a deal with the Clinton administration. Nuclear experts believe that North Korea now has enough weapons-grade plutonium for 10 or 11 nuclear weapons but that it has yet to develop a delivery system for such bombs.
The US has not held any direct talks with North Korea for two years and has imposed unilateral sanctions, including the freezing of a North Korean bank account in Macau. Some administration officials are considering further sanctions, independent of UN action, possibly including the stopping and searching of all ships entering and leaving North Korea.
North Korea's UN ambassador, Pak Gil Yon, said he was proud of the scientists who conducted the test, adding that the security council should congratulate his country for taking an action that would contribute "to the maintenance and guarantee of peace and security in the peninsula and the region".