Preventing the spread and use of nuclear weapons is an enormous security challenge, and there is no more urgent threat to the United States than a terrorist armed with a nuclear weapon. Nuclear weapons materials are stored in dozens of countries, some without proper security. Nuclear technology is spreading. Iran continues its illicit nuclear program , and North Korea’s nuclear weapons program is destabilizing to the region and an urgent proliferation concern. President Obama is working on multiple levels to address these dangers, including through work to strengthen the global nonproliferation and disarmament regime, deal with those states in violation of this regime, and uphold our obligations to work constructively and securely toward the goal of a world without nuclear weapons.