Pope Francis and UN chief Antonio Guterres talked up a global treaty against nuclear weapons that came into force on Friday, although it appears unlikely to spur a quick reduction in stockpiles of doomsday weapons. Campaigners against nuclear arms celebrated as the 2017 Treaty on the Prohibition of Nuclear Weapons (TPNW) came into effect. Mr Guterres hailed it as an "important step" after Pope Francis called on more governments to sign the accord. The treaty has been signed by 86 countries, but the United States, Russia, China and other nuclear-armed powers have not taken part and show no signs of scrapping their atomic arsenals any time soon. “The TPNW is an important step towards the goal of a world free of nuclear weapons and a strong demonstration of support for multilateral approaches to nuclear disarmament,” Mr Guterres said. “Nuclear weapons pose growing dangers and the world needs urgent action to ensure their elimination and prevent the catastrophic human and environmental consequences any use would cause.” Pope Francis voiced support for the treaty on Wednesday, calling on countries to sign up and show determination to achieve the nuclear-free, peaceful world that “humanity needs so very much today”. Anti-nuclear activists around the world marked the treaty coming into force, including members of the International Campaign to Abolish Nuclear Weapons, which won the Nobel Peace Prize in 2017. A petition from survivors of the 1945 atomic bombings of Japanese cities Hiroshima and Nagasaki gathered nearly 14 million signatures in support of the new treaty this month, according to <em>The Asahi Shimbun</em>. The treaty came into force 90 days after it was ratified by Honduras, the 50th country to do so. It prohibits the development, manufacture, possession and use of nuclear arms – effectively banning the weapons. But the treaty has not been signed by – and does not apply to – any of the states that already have nuclear arms: the US, Russia, China, Britain, France, India, Pakistan and North Korea. Officials in the new US administration of President Joe Biden say they aim to extend the New Start arms control treaty with Russia, which limits nuclear warhead deployments by the world’s top two nuclear powers and which expires on February 4. But the Stockholm International Peace Research Institute, an arms watchdog, said in its latest annual report that Russia, the US and other nuclear powers all “continue to modernise their nuclear arsenals”.