UNITED NATIONS - UN Secretary-General Antonio Guterres warned on Wednesday that the expiration of New START, the US-Russia nuclear arms reduction treaty, marks a grave moment for international peace and security.

"For the first time in more than half a century, we face a world without any binding limits on the strategic nuclear arsenals of the Russian Federation and the United States of America, the two states that possess the overwhelming majority of the global stockpile of nuclear weapons," Guterres said in a statement.

New START, which limits the number of deployed nuclear warheads and strategic delivery systems of Russia and the United States, expires on Thursday.

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Throughout the Cold War and its aftermath, nuclear arms control between the two countries helped prevent catastrophe. It built stability and, when combined with other measures, prevented devastating miscalculations. Most importantly, it facilitated the reduction of thousands of nuclear weapons from national arsenals. Strategic arms control drastically improved the security of all people, not least the populations of the United States and Russia, said Guterres.

This expiration of New START could not come at a worse time, as the risk of a nuclear weapon being used is the highest in decades, he said.

"Yet at this moment of uncertainty, we must search for hope. This is an opportunity to reset and create an arms control regime fit for a rapidly evolving context," said Guterres. "I welcome that the presidents of both states have made clear that they appreciate the destabilizing impact of a nuclear arms race and the need to prevent the return to a world of unchecked nuclear proliferation. The world now looks to the Russian Federation and the United States to translate words into action."

Guterres urged the two states to return to the negotiating table without delay and agree on a successor framework that restores verifiable limits, reduces risks and strengthens common global security.

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New START, which entered into force in 2011, was the last arms control pact between Russia and the United States after Washington withdrew from the Intermediate-Range Nuclear Forces Treaty in 2019.