State Dept. Accuses China of Secret 2020 Nuclear Test at Lop Nur

Under Secretary of State Thomas DiNanno publicly accused China on Feb. 6, 2026, of conducting a yield-producing nuclear test at Lop Nur on June 22, 2020. DiNanno told a Washington arms control conference that China used decoupling — detonating a device inside a large underground cavity to suppress seismic output — to keep the blast below detection thresholds. The State Department said the accusation was based on intelligence assessments. CTBTO Executive Secretary Robert Floyd directly disputed the claim, stating the International Monitoring System's 321 stations found no event consistent with a nuclear weapon test on that date. CSIS satellite imagery analysis of Lop Nur found the evidence inconclusive. China categorically denied the accusation. The dispute sharpened congressional debate over whether the U.S. should pursue CTBT ratification to gain on-site inspection rights.