The United States has updated its allegation that China conducted an underground nuclear test in June 2020, providing new details from seismic monitoring data that suggest a possible concealed detonation. Assistant Secretary of State Christopher Yeaw told the Hudson Institute that a remote seismic station in Kazakhstan recorded an explosion of magnitude 2.75 at the Lop Nor test site on June 22, 2020. Yeaw, a former intelligence analyst and nuclear engineer, said the readings were inconsistent with mining operations or natural earthquakes and “what you would expect with a nuclear explosive test.”
The updated claim, however, has not been independently confirmed. The Comprehensive Test Ban Treaty Organization cautioned that the seismic events were far below the threshold required to definitively identify a nuclear test. Executive Secretary Robert Floyd noted that two small seismic events recorded 12 seconds apart were too minor to determine the cause with confidence.
China Washington, Liu Pengyu, described the claim as “entirely unfounded” and accused the U.S. of political manipulation aimed at pursuing nuclear hegemony. China’s last officially acknowledged underground nuclear test occurred in 1996, and, like the U.S., it has signed but not ratified the 1996 Comprehensive Nuclear-Test-Ban Treaty.
The U.S. allegation coincides with efforts by Donald Trump to push China into negotiations with the U.S. and Russia for a successor to the New START treaty, which expired on February 5. Analysts warn that the treaty’s expiration, coupled with China’s expanding nuclear arsenal—estimated by the Pentagon to exceed 600 operational warheads and potentially surpass 1,000 by 2030—raises the risk of a renewed global arms race.
Yeaw suggested that China may have attempted to conceal the alleged test through a technique known as “decoupling,” detonating a device within a large underground chamber to reduce seismic signals. The U.S., which last conducted an underground nuclear test in 1992, now relies on advanced simulations and supercomputers to maintain the reliability of its nuclear stockpile. The updated report, first presented at the Hudson Institute and covered by Reuters, highlights ongoing tensions in nuclear deterrence and the challenges of verifying compliance with international test ban agreements.
