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CNN  — 

White House national security adviser Robert O’Brien on Friday rejected Russian President Vladimir Putin’s proposal to extend New START, a key arms control treaty, for one year without any additional agreements, calling the offer a “non-starter.”

“The United States proposed an extension of New START for one year, in exchange for Russia and the United States capping all nuclear warheads during that period. This would have been a win for both sides, and we believed the Russians were willing to accept this proposal when I met with my counterpart in Geneva,” O’Brien said in a statement released on the White House’s National Security Council Twitter feed.

“President Putin’s response today to extend New START without freezing nuclear warheads is a non-starter,” he said.

He threatened a “costly” arms race if Russia does not come back to the table with a better proposal: “The United States is serious about arms control that will keep the entire world safe. We hope that Russia will reevaluate its position before a costly arms race ensues.”