On 9 October 2006, North Korea performed its first nuclear test, detonating a plutonium-based device underground. The test made North Korea the tenth country to develop and the eighth to openly test nuclear weapons.
On 3 October 2006, North Korea announced its intention to conduct a nuclear test. The blast is generally estimated to have had an explosive force of less than one kiloton, and some radioactive output was detected. United States officials suggested the device may have been a nuclear explosive that misfired.
An anonymous official at the North Korean Embassy in Beijing told a South Korean newspaper that the explosive output was smaller than expected. Because of the secretive nature of North Korea and small yield of the test, there remains some question as to whether it was a successful test of an unusually small device (which would have required sophisticated technology), or a partially failed "fizzle" or dud. A scientific paper later estimated the yield as 0.48 kilotons.
Reportedly the Chinese government was given a 20-minute advance notification that the test was about to occur. China sent an emergency alert to Washington, D.C., through the U.S. Embassy in Beijing at which time President George W. Bush was told by National Security Advisor Stephen Hadley "shortly after" 10 p.m. (UTC-5) that a test was imminent.
North Korea had been suspected of maintaining a clandestine nuclear weapons development program since the early 1980s when it constructed a plutonium-producing Magnox nuclear reactor at Yongbyon, and various diplomatic means had been used by the international community to attempt to limit North Korea's nuclear work to peaceful and scientific means and encouraging North Korea to participate in international treaties. In 1994, the United States and North Korea signed the "Agreed Framework", whereby North Korea agreed to freeze its graphite moderated reactor program in exchange for fuel, moves toward normalization of political and economic relations, and the construction of two modern nuclear power plants powered by light-water reactors. Eventually, North Korea's existing nuclear facilities were to be dismantled, and the spent reactor fuel taken out of the country.
However, in 2002, rumors circulated that North Korea was pursuing both uranium enrichment technology and plutonium reprocessing technologies in defiance of the Agreed Framework. North Korea reportedly told American diplomats in private that they were in possession of nuclear weapons, citing American failures to uphold their own end of the "Agreed Framework" as a motivating force. North Korea later clarified that it did not possess weapons yet, but that it had a right to possess them. In late 2002 and early 2003, North Korea began to take steps to eject International Atomic Energy Agency inspectors while re-routing spent fuel rods for plutonium reprocessing for weapons purposes. Throughout the course of 2003, North Korean and American officials exchanged harsh words and staged military exercises which were interpreted by the other party to be aggressive. As late as the end of 2003, North Korea claimed that it would freeze its nuclear program in exchange for American concessions – in particular a non-aggression treaty – but a final agreement was not reached and talks continued to be cancelled or fall through. North Korea withdrew from the Nuclear Non-Proliferation Treaty in 2003 after not receiving light-water reactors promised by the United States which were going to be delivered in exchange for North Korea not developing their own power plants, as understood in the "Agreed Framework".
In early 2004 former Los Alamos National Laboratory director Siegfried S. Hecker, as part of an unofficial U.S. delegation, was allowed to inspect North Korea's plutonium production facilities. Hecker later testified before the United States Congress that while North Korea seemed to have successfully extracted plutonium from the spent fuel rods, he saw no evidence at the time that they had produced a workable weapon. In 2007, the former senior scientist of Pakistan, Abdul Qadeer Khan claimed that North Korea's nuclear program was well advanced before his visit in 1993 with Benazir Bhutto, former prime minister.
In September 2004, though, North Korean officials announced they had successfully processed Yongbyon plutonium into a workable nuclear deterrent. Through 2005 more diplomatic talks were attempted between the United States, North Korea, South Korea, China, Japan, and Russia (the six-party talks) but little concrete change occurred.
Because North Korea had not conducted a successful test of a nuclear device, the extent of its nuclear weapons program remained ambiguous through 2005 and much of 2006. Though North Korea conducted numerous missile tests (some of which were branded failures by international experts), the question of whether they had actually mastered all aspects of nuclear weapons technology – ranging from material production to complex nuclear weapon design needed to produce the final detonation – remained unanswered. As of 2013 there was agreement in the U.S. intelligence community that North Korea could build a "modest" bomb with a yield of between 6 and 10 kilotons, but disagreement between Defense Intelligence Agency, CIA and the United States State Department over whether it could deploy a miniaturized warhead on a missile.
Rumours of an impending nuclear test circulated during 2005 and early 2006, though none came to immediate fruition. On 3 October 2006, however, North Korea claimed that it would soon conduct a nuclear test, and on 9 October 2006, the state claimed to have successfully conducted a test. The Korean Central News Agency, the state's news agency, issued the following statement:
The field of scientific research in the DPRK successfully conducted an underground nuclear test under secure conditions on October 9, Juche 95 (2006), at a stirring time when all the people of the country are making a great leap forward in the building of a great, prosperous, powerful socialist nation.
It has been confirmed that there was no such danger as radioactive emission in the course of the nuclear test as it was carried out under scientific consideration and careful calculation.
The nuclear test was conducted with indigenous wisdom and technology 100 percent. It marks an historic event as it greatly encouraged and pleased the KPA and people that have wished to have powerful self-reliant defence capability.
It will contribute to defending the peace and stability on the Korean Peninsula and in the area around it.
Later, the North Korean envoy to the UN said it would be better for the Security Council to offer its congratulations rather than pass "useless" resolutions.
On 10 October 2006, an unnamed North Korean official was quoted as saying that North Korea could launch a nuclear missile unless the United States would sit down for face-to-face talks. However, few, if any, military and defense experts believed that the North Koreans possessed the technology to mount a nuclear warhead to a ballistic missile.
On 11 October the Associated Press reported that North Korea had threatened war if attempts would be made to penalize them through further sanctions. This statement occurred even as Japan moved to tighten sanctions on the country. South Korea said they were ensuring their troops were prepared for nuclear war. A U.S. Army major, stationed along the border between North and South Korea, said that the overall situation was "calm" but that "Communist troops were more boldly trying to provoke their southern counterparts: spitting across the demarcation line, making throat-slashing hand gestures, flashing their middle fingers and trying to talk to the troops."
On the day of the test, the North Korean Foreign Ministry stated that "if the U.S. keeps pestering us and increases pressure, we will regard it as a declaration of war and will take a series of physical corresponding measures".