NBC: North Korean nuclear test could happen as early as Tuesday night By Richard Engel, Jim Miklaszewski and Robert Windrem, NBC News North Korea could carry out an underground test of a nuclear weapon as early as Tuesday night as the North's reclusive leadership dramatically tries to up the stakes with the U.S. and the West, U.S. officials told NBC News. U.S. officials say North Korea may already have an arsenal between 12 and a "few dozen" far more advanced weapons, many more than generally believed. The officials couldn't be specific on a date for the test, but they told NBC News they were "100 percent" certain there would be a nuclear test within the next two weeks or "at any time." Tensions between North and South Korea increased this week when Pyongyang threatened to turn Seoul into "ashes." While the North regularly issues such threats, the South seemed to be taking this round of threats more seriously by increasing its security. U.S. and South Korean intelligence agencies have been monitoring test preparations at P'unggye-yok, the North Korean test site near the Chinese border, for the past several weeks. As new evidence of tunneling emerged, officials began to see Army Day celebrations scheduled for Wednesday (Tuesday night in the U.S.) as a possible date for the test. It will be the first time the country's 29-year-old leader, Kim Jong Un, will get a chance to address the Korean People's Army as commander. At the high end of the range, U.S. officials and other researchers said, North Korea may already have up to "a few dozen" nuclear weapons that could be fitted atop its vast fleet of ballistic missiles. Currently, North Korean missiles are limited to an intermediate range, capable of hitting cities in Japan or South Korea but not the United States. What the new test could reveal is an improvement in the type of weapons North Korea has. For the past several years, the U.S. has been monitoring North Korean research into thermonuclear weapons, hydrogen bombs and bombs known as boosted fission weapons, in which plutonium and uranium are combined. David Albright, president of the Institute for Science and International Security, or ISIS, a nonpartisan nuclear arms research group, said Tuesday that the tests may also be about ensuring the reliability of North Korea's current weapons design. "Once you get beyond a dozen, it makes sense to test type and reliability of your weapons," he said. Albright said that his group's estimate of North Korea's weapons stockpile is a bit less than those provided by the U.S. officials but that ISIS, too, believes Pyongyang has "missile-deliverable weapons." North Korea successfully tested nuclear weapons in 2006 and 2009. In both cases, the first word came in statements from the North Korean Foreign Ministry hours before the tests were carried out. No such statement has been issued yet, but a U.S. official said it's possible that this time North Korea wouldn't follow the same protocol. Watch the Top Videos on msnbc.com Ten days ago, North Korea failed in its attempt to launch an observation satellite, a test the U.S. believed was a cover for test of intercontinental missile technology. In response, the U.S. canceled an agreement that would have provided 241,000 tons of nutritional aid, while the U.N. Security Council voted unanimously to "strongly condemn" the failed launch and said it would tighten sanctions against Pyongyang's government. Albright added that North Korea might not want to test its weapons to their full yield in order to avoid another embarrassment, noting that the geology around the test site is fragile and that a large test could aggravate that issue.