UN head Antonio Guterres warned on Monday that the world faced "a nuclear danger not seen since the height of the Cold War" and was just "one miscalculation away from nuclear annihilation".
"We have been extraordinarily lucky so far. But luck is not a strategy. Nor is it a shield from geopolitical tensions boiling over into nuclear conflict," Guterres said at the start of a conference of countries belonging to the nuclear Non-Proliferation Treaty (NPT).
"Today, humanity is just one misunderstanding, one miscalculation away from nuclear annihilation," he said, calling on nations to "put humanity on a new path towards a world free of nuclear weapons".
Guterres's comments came at the opening 10th review conference of the NPT, an international treaty that came into force in 1970 to prevent the spread of nuclear weapons.
The meeting, held at the UN's headquarters in New York, has been postponed several times since 2020 due to the Covid-19 pandemic. It will run until 26 August.
Guterres said the conference was "a chance to strengthen" the treaty and "make it fit for the worrying world around us," citing Russia's war in Ukraine and tensions on the Korean peninsula and in the Middle East.
"Eliminating nuclear weapons is the only guarantee they will never be used," the secretary-general implored, adding that he would visit Hiroshima for the anniversary of the 6 August, 1945 atomic bombing of the Japanese city by the United States.
"Almost 13,000 nuclear weapons are now being held in arsenals around the world. All this at a time when the risks of proliferation are growing and guardrails to prevent escalation are weakening," Guterres added.
In January, the five permanent members of the UN Security Council - the United States, China, Russia, Britain and France - had pledged to prevent the further dissemination of nuclear weapons.
At the last review conference in 2015, the parties were unable to reach agreement on substantive issues.