conducted multiple nuclear weapons tests and issued several threats of war on South Korea. As of April 2018, North Korea along with South Korea have announced their intentions to completely denuclearize the Korean peninsular and finally declare peace between the two Koreas. Cause There has been a great deal of speculation on the nature of the incident. Hypotheses can be divided on several axes. Things that could cause the physical phenomena observed: A large chemical explosive blast. A forest fire. The United States National Security Advisor, Condoleezza Rice, said "maybe it was ... some kind of forest fire". The Yonhap news agency also quoted a source suggesting a forest fire. A natural cumulonimbus cloud formation. If there was an explosion, the main possible causes: Explosive remnants of war. Unexploded ordnance from the Korean War become increasingly unstable as they deteriorate. The United States dropped 635,000 tons of bombs in Korea between 1950 and 1953. North Korea's official explanation of controlled demolition for a hydroelectric project. A nuclear weapon test or demonstration. Recent intelligence reported that North Korea might have been planning its first nuclear bomb test, and the significant date lends credence to this hypothesis. However, it would be unusual for North Korea to then deny it, and international officials have stated that it does not appear to have been a nuclear explosion. (Later updates in intelligence suggested that the test planning may have not been what it appeared to be.) A nuclear accident. Likewise, it has been denied that the explosion was nuclear. A large chemical explosive blast, to calibrate for a later nuclear test. Explosion of a munitions dump, or of explosives in a munitions factory. Finally, another way to divide up explosion hypotheses is by how intentional it was: Intended by North Korea. Accidental. North Korea's failing economy has made its industry accident-prone, as seen in the Ryongchon disaster earlier in 2004. Covert operation by a foreign state. Military or terrorist action connected with an internal power struggle. North Korea's claim to possess nuclear weapons on 10 February 2005 gives the nuclear testing or accident hypotheses some credibility. However, no neighboring nations have claimed any detection of radioactive isotopes which would be characteristic of either. North Korea claimed to have tested its first nuclear weapon on 9 October 2006. There have since been multiple nuclear tests by North Korea. See also North Korea and weapons of mass