The United States has accused China of secretly conducting a nuclear explosive test at the Lop Nur site in June 2020, alleging Beijing used a technique known as "decoupling" to muffle seismic signals, a charge China has rejected as "completely groundless" amid mounting tensions over the collapse of global arms-control agreements.
The allegation was made public by Under Secretary of State Thomas DiNanno at a United Nations disarmament conference in Geneva on Feb. 6, 2026. "I can reveal that the US government is aware that China has conducted nuclear explosive tests, including preparing for tests with designated yields in the hundreds of tons," DiNanno said, according to NPR. He added, "China has used decoupling - a method to decrease the effectiveness of seismic monitoring - to hide its activities from the world."
Days later, Assistant Secretary of State Christopher Yeaw cited seismic data during remarks at the Hudson Institute. A monitoring station in Kazakhstan detected a magnitude 2.75 seismic event roughly 450 miles from Lop Nur on June 22, 2020. "There is very little possibility that it is anything other than an explosion, a singular explosion," Yeaw said, according to Newsweek.
The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), however, offered a more cautious assessment. Executive Secretary Robert Floyd confirmed the network recorded "two very small seismic events, 12 seconds apart" that day. "With this data alone, it is not possible to assess the cause of these events with confidence," Floyd said.
The CTBTO's monitoring system can typically detect nuclear explosions of about 500 tons of TNT equivalent or greater. The June 2020 signals fell below that threshold. A satellite analysis by the Center for Strategic and International Studies found it "did not provide any conclusive findings to support or disprove the recent US allegations," noting the vastness of the Lop Nur testing area.
Beijing responded forcefully. Foreign Ministry spokesperson Lin Jian said, "The US accusation of Chinese nuclear explosive tests is completely groundless." He added, "China opposes the US fabrication of pretexts for its own resumption of nuclear tests." Chinese Embassy spokesperson Liu Pengyu called the claim "entirely unfounded" and accused Washington of "political manipulation aimed at pursuing nuclear hegemony."
The dispute unfolds at a precarious moment for nuclear arms control:
- The New START treaty between the U.S. and Russia expired on Feb. 5, 2026
- President Donald Trump said in October 2025 the U.S. would consider resuming testing "on an equal basis"
- The Pentagon estimates China's nuclear stockpile has grown from roughly 200-300 warheads in 2019-2020 to more than 600 today, with projections exceeding 1,000 by 2030
United Nations Secretary-General António Guterres described the expiration of New START as "a grave moment for international peace and security."
Analysts remain divided. Tong Zhao of the Carnegie Endowment for International Peace told NPR the allegations appear "consistent with the very active status of China's Lop Nur nuclear testing site over many years." By contrast, Daryl Kimball of the Arms Control Association warned a U.S. return to testing would be "technically unnecessary."
Jeffrey Lewis of the Middlebury Institute calculated on X that a magnitude 2.7 event could correspond to roughly 18 tons of yield, or 400-700 tons if fully decoupled-far smaller than the roughly 20,000-ton yield of the Nagasaki bomb.
