Weapon of mass destruction
The only country to have used a nuclear weapon in war is the United States, which dropped two atomic bombs on the Japanese cities of Hiroshima and Nagasaki during World War II. There are eight countries that have declared they possess nuclear weapons and are known to have tested a nuclear weapon, only five of which are members of the NPT. The eight are China, France, India, North Korea, Pakistan, Russia, the United Kingdom, and the United States.
Southeast Asian Nuclear-Weapon-Free Zone Treaty
The treaty includes a protocol under which the five nuclear-weapon states recognized by the Treaty on the Non-Proliferation of Nuclear Weapons (NPT), namely China, the United States, France, Russia and the United Kingdom (who are also the five permanent members of the United Nations Security Council) undertake to respect the Treaty and do not contribute to a violation of it by State parties. None of the nuclear-weapon states have signed this protocol.