GENEVA (AP) — A U.S. official focusing on arms control has provided what he called new, declassified details of a Chinese underground nuclear test nearly six years ago. Also Monday, the assistant secretary of state for the bureau of arms control and nonproliferation urged countries to press China and Russia to do more on nuclear disarmament. He spoke to a U.N.-backed body after the last nuclear arms pact between the United States and Russia expired this month. He says Beijing has “massively expanded” its nuclear arsenal and pointed to an explosion detected at an underground site in western China on June 22, 2020. Beijing denies carrying out a nuclear test and balks at restrictions on its smaller but growing nuclear arsenal.