U.S. Official Alleges China Conducted Underground Nuclear Test at Lop Nor in 2020

A senior U.S. official has alleged that China carried out a covert underground nuclear test in June 2020 at its Lop Nor test site in western China, raising fresh concerns about global nuclear security and arms control. Assistant Secretary of State Christopher Yeaw disclosed the claim during an event at the Hudson Institute in Washington, stating that seismic data pointed to a possible nuclear explosion.

According to Yeaw, a remote seismic monitoring station in Kazakhstan detected a magnitude 2.75 event on June 22, 2020, approximately 450 miles from Lop Nor. After reviewing additional seismic data, Yeaw asserted that the signal was highly unlikely to be caused by mining activity or a natural earthquake. He said the characteristics of the seismic event were consistent with what experts would expect from a nuclear explosive test. Yeaw also suggested that China may have attempted to conceal the blast using a technique known as “decoupling,” in which a nuclear device is detonated inside a large underground cavity to reduce detectable shockwaves.

However, the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), which operates a global monitoring system to detect nuclear test explosions, stated that the available data were insufficient to confirm the allegation. The CTBTO reported that two small seismic events, occurring 12 seconds apart, were recorded that day. These events were well below the organization’s detection threshold of 500 metric tons of TNT equivalent, making it difficult to determine their cause with confidence.

China has firmly denied conducting any nuclear testing, calling the U.S. accusation “entirely unfounded” and politically motivated. Beijing emphasized its commitment to the global ban on nuclear tests, despite having signed but not ratified the Comprehensive Nuclear-Test-Ban Treaty. The United States has also signed but not ratified the treaty and last conducted an underground nuclear test in 1992.

The allegations come amid heightened tensions following the expiration of the New START treaty between the U.S. and Russia, fueling concerns about a renewed global nuclear arms race.