UNITED NATIONS (Reuters) - The pursuit of nuclear weapons will not bring security for North Korea’s government and China’s assistance is vital to bringing Pyongyang’s atomic and missile programs under control, U.S. Secretary of State Rex Tillerson said on Thursday. “North Korea may assume that nuclear weapons will ensure the survival of its regime. In truth, nuclear weapons are clearly only leading to greater isolation, ignominy and deprivation,” Tillerson said at the U.N. Security Council.  “If China truly desires to denuclearize the Korean peninsula to promote stability and to avoid conflict in that sensitive region right on its own border, now’s the time to work with the rest of us ... to put the kind of pressure on North Korea that can change its strategic calculations before it’s too late,” he added. 