North Korea on Tuesday again flouted international rules by detonating its third atomic device in less than a decade, Reuters reported.
Pyongyang's action was swiftly and roundly condemned by the international community, with the U.N. Security Council convening an emergency session to discuss an appropriate punishment.
The international organization that monitors for nuclear tests said it detected a seismic event measuring 5.0 in magnitude in North Korea. That is roughly double the seismic movement produced by the North's previous tests in 2006 and 2009, according to the Preparatory Commission for the Comprehensive Test Ban Treaty Organization.
"We can assume this is roughly twice as big in magnitude" as the last test, Lassina Zerbo, who heads the international data center division of the test ban body, was quoted by Reuters as telling reporters.
Definitive proof that a nuclear explosion took place will be if the CTBTO network's air monitoring stations also pick up unusual levels of radionuclides. "We cannot say anything about that before two to three days minimum," Zerbo said.
The underground nuclear blast at the Punggye-ri test site had been widely anticipated for months. Satellites monitoring the facility had consistently shown concerted preparations for an atomic trial and the Kim Jong Un regime had repeatedly threatened to carry out another test.
The Stalinist state on Tuesday boasted of a successful test that had "greater explosive force" than its two prior blasts. Regime-controlled media said the test involved a "miniaturized" device, which suggests the detonation involved plutonium and not weaponized uranium as had been widely speculated.
The North defended its nuclear test as necessary in the face of "U.S. hostility" and warned of additional actions if it is punished. "If the United States continues to come out with hostility and complicates the situation, we will be forced to take stronger, second and third responses in consecutive steps," an unidentified North Korean Foreign Ministry official said through state media.
The United States, Japan, South Korea, Russia, and China all condemned the test, as did U.N. Secretary General Ban Ki-moon, NATO, the European Union, and the International Atomic Energy Agency.
"The danger posed by North Korea's threatening activities warrants further swift and credible action by the international community. The United States will also continue to take steps necessary to defend ourselves and our allies," President Obama said in released remarks.
"This deserves only one thing and that is a one-sided condemnation. North Korea is likely the most horrible country on this planet," Reuters quoted Danish Foreign Minister Villy Sovndal as saying.
It could take weeks for the Security Council to hammer out new economic penalties, Reuters quoted delegates as saying.
North Korea's ambassador to Beijing was ordered to appear before Chinese officials to receive its protest of the test, according to the Chinese Foreign Ministry. Beijing is "strongly dissatisfied and resolutely opposed" to the nuclear trial and called on Pyongyang to "stop any rhetoric or acts that could worsen situations and return to the right course of dialogue and consultation as soon as possible," Reuters quoted Foreign Minister Yang Jiechi as saying.
China is the North's primary economic benefactor and a veto-holding permanent member of the Security Council. Its support is critical if any new sanctions resolution is to be passed in New York.
North Korea is already the world's most internationally isolated country and has been under punitive Security Council sanctions for years as punishment for its continued nuclear arms and ballistic missile activities. The latest test could be another step toward development of a nuclear warhead small enough to be fitted onto a missile.
"This latest test and any further nuclear testing could provide North Korean scientists with additional information for nuclear warhead designs small enough to fit on top of its ballistic missiles," the Associated Press quoted Daryl Kimball and Greg Thielmann of the Arms Control Association as stating in an online post. "However, it is likely that additional testing would be needed for North Korea to field either a plutonium or enriched uranium weapon."
The explosive force of Tuesday's test is projected by the South Korean military to have been approximately 6-7 kilotons, according to the Yonhap News Agency. That conclusion was drawn from analysis of the geologic shock waves produced from the blast.
Though the initial estimated yield is fairly small by the standards of other nuclear weapon possessor countries, it is slightly bigger than the yields of North Korea's two previous tests. The 2006 trial had an estimated yield of 1 kiloton, leading many foreign analysts to assess it as a failure, and the 2009 blast had a projected yield of between 4 and 6.9 kilotons.
As the North expelled all international weapon monitors in 2009, little is definitively known about the country's current fissile material stockpile. It is believed that the Stalinist state possess enough plutonium to fuel between four and eight warheads, Kimball and hielmann, wrote for the Arms Control Association on Tuesday.
Though Pyongyang possesses a uranium enrichment program, there is no publicly available information about the amount, if any, of material it has enriched to weapon-grade levels of around 90 percent.
A senior North Korean diplomat told the international Conference on Disarmament on Tuesday that his government would never submit to international rulings that it desist its nuclear weapons development, Reuters separately reported.