The last remaining nuclear arms pact between Russia and the United States is set to expire this week, removing any caps on the two largest atomic arsenals for the first time in more than a half-century. The end of the New START Treaty sets the stage for what many fear could be an unconstrained nuclear arms race. Russian President Vladimir Putin has declared his readiness to stick to the treaty's limits for one more year if Washington follows suit, but U.S. President Donald Trump has been noncommittal about extending it. Arms control advocates have warned that the treaty's termination would fuel a renewed arms race.

President Donald Trump has appeared to suggest on social media that the U.S. resume testing nuclear weapons for the first time in three decades. There was no indication that the U.S. would start detonating warheads, but the president offered few details about what seemed to be a significant shift in U.S. policy. He made the announcement on social media minutes before meeting with Chinese leader Xi Jinping on Thursday in South Korea. The U.S. military already regularly tests its missiles that are capable of delivering a warhead, but it has not detonated the weapons since 1992 because of a test ban.