A global treaty banning nuclear weapons is set to be adopted at the United Nations today despite opposition from the United States, Britain, France and other nuclear powers that boycotted negotiations. <br/><br/>Supporters describe the treaty as a historic achievement but the nuclear-armed states have dismissed the ban as unrealistic, arguing it will have no impact on reducing the global stockpile of 15,000 nuclear weapons. <br/><br/>Led by Austria, Brazil, Mexico, South Africa and New Zealand, 141 countries have taken part in three weeks of negotiations on the treaty that provides for a total ban on developing, stockpiling or threatening to use nuclear weapons. Advocates hope it will increase pressure on nuclear states to take disarmament more seriously. <br/><br/>None of the nine countries that possess nuclear weapons — the United States, Russia, Britain, China, France, India, Pakistan, North Korea and Israel took part in the negotiations.