North Korea: Readying nuclear test

North Korea appears to be readying a fourth underground nuclear test at the same site where it conducted one eight weeks ago, a South Korean official said. \"We have detected increased activity of labor forces and vehicles at the southern tunnel of the test site in Punggye-ri [nuclear test site], where the regime has worked on maintenance for facilities since its third nuclear test in February,\" a high-ranking South Korean government official told the South Korean newspaper JoongAng Ilbo. \"The activities appear to be similar to those before the third test, so we are closely monitoring the site,\" the official said. The third test in seven years Feb. 12 produced a magnitude-5.1 tremor that exhibited a nuclear bomb signature, national and international scientific agencies, including the U.S. Geological Survey, said. \"We were also tipped off that Pyongyang would soon carry out an additional nuclear test,\" the official said. \"But we are analyzing if it is indeed preparation for an additional test or it is just to pressure Seoul and Washington.\" The tunnels bored into the granite southern side of Mount Mantap, where detonations also took place in 2006 and 2009, are believed to be 7 to 10 feet high and wide and hundreds of yards long, South Korea\'s Defense Ministry said in February. Political prisoners were forced to dig the tunnels, South Korea\'s The Chosun Ilbo newspaper reported. North Korea\'s Hwasong concentration camp is located near the mountain. A high-ranking South Korean Defense Ministry official told the JoongAng Ilbo the North could test the nuclear device at any time. A military official told the JoongAng Ilbo Pyongyang also appeared to be preparing to launch a medium-range missile with a range of about 2,000 miles. The reports came hours after Seoul warned that Pyongyang could launch a medium-range missile test around Wednesday, ahead of the anniversary of founding North Korean President Kim Il Sung\'s birthday April 15. The warning came three days after South Korea\'s defense minister said the North had moved a missile with a \"considerable range\" to its east coast. The missile -- which South Korean media said was likely a BM25 Musudan intermediate-range ballistic missile -- would possibly be used \"for demonstration or for training,\" Defense Minister Kim Kwan-jin told Parliament Thursday. The Musudan\'s 2,000-mile range could threaten South Korea, Japan and Southeast Asia, and possibly U.S. forces in Guam, South Korean officials and analysts said. Guam is about 2,200 miles from North Korea. It is not capable of reaching the mainland United States, officials said. To avoid escalating tensions, Washington has delayed a Minuteman III intercontinental ballistic missile test originally scheduled for Tuesday at Vandenberg Air Force Base near Lompoc, Calif., a senior Defense official said. The test had nothing to do with North Korea, but Washington decided to hold off \"given recent tensions,\" the official told CNN. Chinese President Xi Jinping referred indirectly to the crisis Sunday, saying, \"No one should be allowed to throw a region and even the whole world into chaos for selfish gains.\" While pursuing its own interests, a country should accommodate the legitimate interests of others,\" he said at a regional business forum in Boao, China, near Qionghai, adding the international community and its collective scrutiny should be a platform for common development rather than an \"arena where gladiators fight each other.\" Western diplomats attending the conference said Xi\'s intentionally ambiguous wording appeared to be a veiled warning to Pyongyang but could also have been partly directed at Washington, The Financial Times said. Beijing often accuses Washington of meddling in the region. China\'s Foreign Ministry issued a separate statement repeating it was \"seriously concerned\" about the \"continuously escalating tensions\" on the Korean Peninsula. Switzerland, meanwhile, offered to act as a mediator if that would \"contribute to a de-escalation on the Korean Peninsula,\" a Swiss Foreign Ministry spokeswoman said in a statement. Bern was recently in contact with Pyongyang but no talks are planned, she said.