Washington on Monday accused China of dramatically swelling its nuclear arsenal, and doubled down on claims that Beijing has conducting secret nuclear tests, demanding again it be part of any future arms control treaty. Washington said the lapsing earlier this month of New START -- the last treaty between top nuclear powers the United States and Russia -- presented the possibility to achieve a “better agreement,” including Beijing.For all the latest headlines follow our Google News channel online or via the app.China has publicly rejected calls to enter negotiations on a new three-way treaty.Christopher Yeaw, the US assistant secretary of state for arms control and nonproliferation, told the Conference on Disarmament in Geneva that the New START treaty had been seriously flawed.“Perhaps its greatest flaw was that New Start did not account for the unprecedented, deliberate, rapid and opaque nuclear weapons build-up by China,” he said.“Despite its claims to the contrary, China has