US Ambassador to the United Nations Nikki Haley has said the regimes that most threaten the world today with weapons of mass destruction — North Korea, Iran and Syria — also promote conflict and regional instability and "aid terrorists and militant groups." Haley called Iran on Thursday "the leading cause of instability in an unstable part of the world." Tehran supports "terrorists, proxy militants and murderers like (the head of the Syrian regime) Bashar Assad,” she told the UN Security Council that met on confidence-building measures to tackle the proliferation of weapons of mass destruction. Haley said the international community must respond to Irans "dangerous violations" of its obligations in the UN resolution endorsing the nuclear deal, "not because we want the nuclear deal to fail, but because we want the cause of nonproliferation to succeed." The diplomat also said that North Korea poses the greatest threat to nuclear proliferation and is continuing "its reckless pursuit of nuclear weapons ... while its people starve and to threaten other nations while intimidating its own citizens." Haley accused Russia of vetoing three council resolutions and preventing the Organization for the Prohibition of Chemical Weapons from holding Assads regime accountable for the use of chemical weapons in Syria.