North Korea Conducts Third Controversial Nuke Test North Korea conducted a nuclear test at an underground site in the remote northeast Tuesday, taking an important step toward its goal of building a bomb small enough to be fitted on a missile that could reach United States. North Korea made clear that the explosion of its third atomic device - which it claimed was smaller than the ones in its previous two tests - was a warning to what it considers a hostile United States. Its actions drew immediate condemnation from Washington, the U.N. and others. Even its only major ally, China, voiced opposition. "The test was conducted in a safe and perfect way on a high level, with the use of a smaller and light A-bomb, unlike the previous ones, yet with great explosive power," North Korea's official Korean Central News Agency said. It was a defiant response to U.N. orders to shut down atomic activity or face more sanctions and international isolation, as well as a direct message from young leader Kim Jong Un to the United States, Pyongyang's No. 1 enemy since the 1950-53 Korean War. KCNA said the test is aimed at coping with "the ferocious hostile act of the U.S." That's a reference to what Pyongyang said was Washington's attempts to block its right to launch satellites. North Korea was punished by U.N. sanctions after a December launch of a rocket that the U.N. and Washington called a cover for a banned missile test. The timing was significant. The test in an underground tunnel came hours before President Barack Obama was scheduled to give his State of the Union speech, a major, nationally televised address. Obama said in a statement Tuesday that the test is "a highly provocative act" and promised to "continue to take steps necessary to defend ourselves and our allies." The test also comes only days before the Saturday birthday of Kim Jong Un's father, late leader Kim Jong Il, whose memory North Korean propaganda has repeatedly linked to the country's nuclear ambitions. This year also marks the 60th anniversary of the signing of the armistice that ended the 1950-53 Korean War, and in late February South Korean President-elect Park Geun-hye will be inaugurated. If the test was indeed successful, as claimed, it would take North Korean scientists a step closer to building a warhead small enough to be mounted on a long-range missile that can reach U.S. shores - seen as the ultimate goal of North Korea's nuclear program. Still, it wasn't immediately clear to outside experts whether the device exploded Tuesday was small enough to fit on a missile, and whether it was fueled by plutonium or highly enriched uranium. In 2006, and 2009, North Korea is believed to have tested devices made of plutonium. But in 2010, Pyongyang revealed a program to enrich uranium, which would give the country a second source of bomb-making materials - a worrying development for the U.S. and its allies. Plutonium facilities are large and produce detectable radiation, making it easier for outsiders to find and monitor. However, uranium centrifuges can be hidden from satellites, drones and nuclear inspectors in caves, tunnels and other hard-to-reach places. Highly enriched uranium also is easier than plutonium to engineer into a weapon.