Explanation:

It's not within United Nations. 
• The International Atomic Energy Agency is an international organization that seeks to promote the peaceful use of nuclear energy, and to inhibit its use for any military purpose, including nuclear weapons.
• The NPT is a landmark international treaty whose objective is to prevent the spread of nuclear weapons and weapons technology, to promote cooperation in the peaceful uses of nuclear energy and to further the goal of achieving nuclear disarmament and general and complete disarmament.
• The Treaty on the Prohibition of Nuclear Weapons, or the Nuclear Weapon Ban Treaty, is the first legally binding international agreement to comprehensively prohibit nuclear weapons, with the goal of leading towards their total elimination. It was passed on 7 July 2017. In order to come into effect, signature and ratification by at least 50 countries is required. For those nations that are party to it, the treaty prohibits the development, testing, production, stockpiling, stationing, transfer, use and threat of use of nuclear weapons, as well as assistance and encouragement to the prohibited activities. For nuclear armed states joining the treaty, it provides for a time-bound framework for negotiations leading to the verified and irreversible elimination of its nuclear weapons programme.
• The African Nuclear Weapon Free Zone Treaty, also known as the Treaty of Pelindaba (named after South Africa's main Nuclear Research Centre, run by The South African Nuclear Energy Corporation and was the location where South Africa's atomic bombs of the 1970s were developed, constructed and subsequently stored), establishes a Nuclear-Weapon-Free Zone in Africa. The treaty was signed in 1996 and came into effect with the 28th ratification on 15 July 2009.