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.
Nuclear weapons and Israel
However, Israel maintains a policy of deliberate ambiguity, never officially denying nor admitting to having nuclear weapons, instead repeating over the years that "Israel will not be the first country to introduce nuclear weapons to the Middle East". Israel has also declined to sign the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) despite international pressure to do so, saying that would be contrary to its national security interests.