"The threat of the use, intentional or otherwise, of nuclear weapons is growing," the UN's representative for disarmament affairs, Izumi Nakamitsu, told a preliminary review meeting of the Nuclear Non-Proliferation Treaty (NPT).
The United States, which holds one of the world's largest nuclear arsenals, also warned the conference that the prospects for progress on disarmament was currently "bleak".
The NPT, introduced at the height of the Cold War a half century ago, seeks to prevent the spread of atomic weapons while putting the onus on nuclear states to reduce their stockpiles.
Speaking at the opening of the Geneva meeting, Nakamitsu warned that "the world today faces similar challenges to the context that gave birth to the NPT."
The NPT treaty, which counts 191 state parties, faces a comprehensive review every five years, with preparatory committees each year in between.
The next full review of the treaty is scheduled for 2020.
The year's meeting comes after North Korea, which pulled out of the treaty 15 years ago, declared a moratorium on nuclear and long-range missile tests and said it would dismantle its nuclear test site.
'Keep pressure' on Pyongyang
Other speakers at the opening of the Geneva meeting, including the European Union representative, stressed the need to "keep pressure" on North Korea.
And Christopher Ford, US Assistant Secretary for International Security and Nonproliferation, insisted that Pyongyang had "yet to return to compliance" of the NPT.
North Korea's nuclear programme was one reason why "the nonproliferation regime today faces great threats," he said, also pointing to Iran's nuclear programme.
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