 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.