Pakistan, Feb. 6 -- The last remaining nuclear arms pact between Russia and the United States expired Thursday, removing any caps on the two largest atomic arsenals for the first time in more than a half-century.

The termination of the New START Treaty could set the stage for what many fear could be an unconstrained nuclear arms race.

Russian President Vladimir Putin last year declared readiness to stick to the treaty's limits for another year if Washington follows suit, but US President Donald Trump has been noncommittal about extending it. He has indicated that he wants China to be a part of it - a push Beijing has rebuffed.

Putin discussed the pact's expiration with Chinese leader Xi Jinping on Wednesday, Kremlin adviser Yuri Ushako...