Washington – US President Barack Obama and his administration are scrambling to forge a unified world reaction to North Korea’s most recent test of a nuclear device, and the strategy has already reaped swift support from normally reluctant Moscow and Beijing.

Russia and China, traditionally North Korea’s strongest allies on the UN Security Council, went along on Monday with the immediate and strong condemnation issued by the 15-member panel, and the council is expected to consider sanctions and other measures in the coming days.

“I think we were all impressed with the fact that the Russians and the Chinese denounced this so strongly,” Rahm Emanuel, Obama’s chief of staff, was quoted as saying by the New York Times.

The early Monday morning explosion, which measured 4.5 to 4.7 on the Richter scale, is expected to be followed by more rocket tests similar to the one Pyongyang launched in April, presenting the Obama administration with its first full-blown crisis with a nuclear country.

While his predecessor George W Bush intensified diplomatic efforts after North Korea tested its first nuclear device in 2006, it appeared that Obama was considering a tougher reaction this time around.

In a statement just hours after the blast, Obama condemned North Korea as a “threat to international peace and security,” adding: “The danger posed by North Korea’s threatening activities warrants action by the international community.”

He vowed the US would “stand up to this behaviour” and added later in the day that North Korea’s actions had “flown in the face of United Nations resolutions, as a result North Korea is not only deepening its own isolation, but it is also inviting stronger international pressure.”

US Secretary of State Hillary Clinton stressed the “importance of a strong, unified approach” in her phone calls to her counterparts in the six-party talks – Japan, Russia, China and South Korea, the countries that have been working for several years to get Pyongyang to dismantle its nuclear programme.

Obama also personally spoke with the leaders of South Korea and Japan Monday to reassure them that the US was committed to their security and to coordinate world reaction. In the calls, Obama called for “a collective response” by the international community, and for concrete measures from the Security Council to “curtail North Korea’s nuclear and missile activities.”

South Korean President Lee Myung Bak and Obama agreed in the call “that the test was a reckless violation of international law that compels action in response,” according to a statement released by the White House.

In the call with Japanese Prime Minister Taro Aso, the two leaders said they would intensify coordination within the six-party talks.

Russia’s ambassador to the United Nation, Vitaly Churkin, who chairs the council this month, criticized North Korea for violating UN resolutions, the nuclear Non-Proliferation Treaty and the Comprehensive Nuclear Test Ban Treaty.

“We are one of the founding fathers, Russia is, of those documents,” Churkin was quoted as saying by Voice of America. “So we think they are extremely important in current international relations. So anything which would undermine the regimes of those two treaties is very serious and needs to have a strong response to it.”

North Korea’s nuclear test pushed South Korea on Tuesday into joining the US-led Proliferation Security Initiative (PSI,) the high seas interdiction programme set up in 2003 by more than a dozen countries which gives international law backing to seizing illegal weapons of mass destruction.

The initiative was set up after 15 missiles were found on board a North Korean freighter, which had to be released for want of international law.

Seoul had previously hesitated to join PSI, saying the move could create unnecessary tension with North Korea, which is under suspicion of trafficking weapons, drugs and counterfeit money. Pyongyang earlier declared that it would regard Seoul’s participation in the PSI a declaration of war, the Yonhap news agency reported. Obama expressed appreciation for South Korea’s support of PSI when he talked to the prime minister, according to a statement from the White House.

The White House said that Pyongyang gave it about an hour’s notice before the 0100 GMT Monday test, which it estimated was “a few kilotons” in strength.

While the response of condemnation kept Obama working well past midnight and into early Monday morning, just hours later he laid a memorial wreath at the Tomb of the Unknowns at the military’s burial grounds, Arlington National Cemetery, to commemorate US Memorial Day, and then played more than four hours of golf.

The notice about the upcoming test from Pyongyang to Washington came about 0000 GMT Monday, with no definitive mention of time. The United States immediately notified the governments of Japan, South Korea, China, and Russia of the warning, according to a White House statement.

“Less than one hour” later, the 0100 GMT explosion was registered by the US Geological Survey, close to the site of North Korea’s 2006 test of a nuclear device, the official said.

The US official was skeptical about any claims by North Korea of the size of the explosion, which registered at 4.7 on the Richter scale by the USGS. Asian monitors registered a 4.5-level temblor.

“We have also seen the North Korean claims of the size of the test and note that in 2006 North Korea vastly overstated the size of that test,” an official who spoke on condition of anonymity said in the statement.

The US government said analysis was being carried out over the coming days.

With the test, Pyongyang, which also appeared to have test-fired a short-range missile early Monday, was making good on earlier threats issued after the Security Council criticized a rocket launch by Pyongyang in April.

Obama declared that the detonation would deepen the Stalinist state’s isolation and vowed the US would “redouble our efforts toward a more robust nonproliferation regime that all countries have responsibilities to meet.”

“In this effort the United States will never waiver from our determination to protect our people and the peace and security of the world,” Obama declared.(dpa)