North Korean nuclear site shows increased activities

North Korea has increased activities at its undergroundnuclear site ahead of US President Barack Obama's upcoming Asia trip, YonhapNews Agency reported Monday, citing military sources. "The Punggye-ri nuclear testsite has shown increased movement of vehicles and forces compared to the past," asenior military official was quoted as saying. "South Korean and US forces havebeen closely monitoring the latest development to detect signs of another test." Thelatest move comes as Obama is set to visit South Korea from Friday to Saturday as part of his Asia trip, which will also include stops in Japan, Malaysia and thePhilippines. Earlier this month, Pyongyang threatened to conduct a "new form" ofnuclear test in protest of joint South Korea-US military exercises. The annual drillsended on Friday. On Monday, North Korea's Foreign Ministry warned that Obama'strip to South Korea could "escalate confrontation and bring the dark clouds of anuclear arms race." The North conducted three nuclear tests in 2006, 2009 and 2013in an apparent effort to make a warhead small enough to fit on a missile. Manyexperts, however, estimate the North has not yet mastered the miniaturizationtechnology. "While increased movement of vehicles could be one of the early signsof an atomic test, signs of an imminent test have not been detected yet," saidanother military official. Shortly before the test in February 2013, the North set upmeasuring equipment and communication cables and sealed up the blast tunnel atthe sprawling test site.