The Treaty on the Non-Proliferation of Nuclear Weapons (NPT), which was signed on 1 July 1968 in London, Moscow and Washington and came into force on 5 March 1970, is based on three pillars: non-proliferation, disarmament and the peaceful use of nuclear energy. It prohibits the five nuclear-weapon states (NWS) — those who have exploded a nuclear device prior to 1 January 1967 (the United States, the USSR, the United Kingdom, China and France) — from delivering material or intelligence to non-nuclear weapon states (NNWS). The non-nuclear weapon states undertake not to manufacture or seek to acquire nuclear weapons. The International Atomic Energy Agency (IAEA) is to verify that each state party to the treaty honours its commitments.