The United States has accused China of secretly conducting nuclear explosive tests just as the last major U.S.-Russia arms control treaty, New START, has expired, raising fears of a new era of unconstrained great‑power nuclear competition. U.S. arms control envoy Thomas DiNanno alleges that China carried out at least one covert test in 2020 and used techniques to mask seismic signals, claims Beijing strongly rejects as false and politically motivated, while China urges Washington to maintain nuclear limits and Russia pushes for a broader, future treaty that would also include China.