Officers walk towards a gateway which leads to the Kaesong Industrial Complex (KCI) at the South's CIQ (Customs, Immigration and Quarantine), just south of the demilitarised zone separating the two Koreas, in Paju, north of Seoul April 8, 2013. Activity in North Korea appears to show it is preparing for a fourth nuclear test, with movement at its atomic test site similar to events preceding earlier blasts, a newspaper reported on Monday, quoting a senior South Korean government official. REUTERS/Kim Hong-Ji (SOUTH KOREA - Tags: MILITARY POLITICS)