UN Secretary-General António Guterres has warned that the expiration of the New START nuclear arms control treaty between the United States and Russia marks a grave moment for international peace and security. In a statement issued on Wednesday, he said the treaty’s expiry at midnight on February 5 effectively removed legal limits on the world’s two largest nuclear powers for the first time in over half a century.

Guterres noted that the US and Russia possess the vast majority of the world’s nuclear weapons and that their bilateral arms control frameworks have long served as a vital pillar of global stability. He recalled that agreements from the Strategic Arms Limitation Talks to New START had enabled the reduction of thousands of nuclear weapons, strengthening global security.

Warning that the collapse of decades of progress comes amid heightened geopolitical tensions and technological change, Guterres said the risk of nuclear use is now at its highest in decades. He urged both nations to return to negotiations and establish a new verifiable framework to restore limits, reduce risks, and reinforce collective security.