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 SEANWFZ treaty has a protocol that is open to signature by the five recognized nuclear-weapon states: China, France, Russia, the United Kingdom, and the United States. The protocol commits those states not to contribute to any violation of the treaty and not to use or threaten to use nuclear weapons within the zone.