FILE PHOTO: United Nations Secretary General Antonio Guterres delivers the opening address at the 73rd session of the United Nations General Assembly at U.N. headquarters in New York, U.S., September 25, 2018. REUTERS/Shannon Stapleton

GENEVA (Reuters) - U.N. Secretary-General Antonio Guterres urged the United States and Russia on Monday to preserve the Intermediate-Range Nuclear Forces Treaty and to extend the New START Treaty before it expires in 2021.

To lose the INF would make the world a more insecure and unstable place, he told the Conference on Disarmament at the United Nations in Geneva. Washington announced on Feb. 1 that it will withdraw from the treaty in six months unless Moscow ends its alleged violations.

“We simply cannot afford to return to the unrestrained nuclear competition of the darkest days of the Cold War. I call on the parties to the INF Treaty to use the time remaining to engage in sincere dialogue on the various issues that have been raised. It is very important that this treaty is preserved.”

He said New START was the only international legal instrument limiting the size of the world’s two largest nuclear arsenals, and its inspection provisions benefited the entire world, noting that global stockpiles of nuclear weapons were one-sixth of what they had been in 1985.

“I urge Russia and the United States to use the time provided by an extension to the treaty to consider further reductions in their strategic nuclear arsenals. I dream of the day when these bilateral arrangements become multilateral.”

He also said he hoped a U.S.-North Korean nuclear summit this week would produce real progress.

“At their summit in Hanoi later this week, I hope that the leaders of the Democratic People’s Republic of Korea and the United States agree to concrete steps for sustainable, peaceful and complete and verifiable denuclearization of the Korean Peninsula”.