A senior U.S. State Department official presented new seismic analysis on February 17, 2026, claiming it strongly indicates China conducted an underground nuclear explosion in June 2020 at its Lop Nur test site in Xinjiang.
Assistant Secretary of State Christopher Yeaw, speaking at an event hosted by the Hudson Institute think tank, described data from a remote monitoring station in Kazakhstan that detected a magnitude 2.75 event on June 22, 2020. The signal originated approximately 450 miles (720 km) away, aligning with the location of China's historic nuclear testing grounds at Lop Nur.
Yeaw, who holds a doctorate in nuclear engineering and has personally reviewed the data, stated there is "very little possibility... that it is anything but an explosion, a singular explosion." He emphasised that the seismic wave characteristics were "quite consistent with what you would expect from a nuclear explosive test" and inconsistent with natural earthquakes or mining blasts.
The disclosure builds on earlier U.S. accusations leveled earlier this month. On February 6, Under Secretary of State Thomas DiNanno told the UN Conference on Disarmament in Geneva that the U.S. believes China has conducted nuclear explosive tests, including preparations for yields in the hundreds of tons, and employed "decoupling" techniques to muffle seismic signals and conceal activities. DiNanno specifically cited the June 22, 2020, event as a "yield-producing nuclear test."
These claims emerge amid escalating U.S.-China tensions over nuclear capabilities and the recent expiration of the New START treaty with Russia. President Donald Trump has indicated willingness to resume U.S. nuclear testing "on an equal basis" to counter perceived asymmetries with China and Russia. Yeaw reiterated this stance at the Hudson Institute, saying the U.S. would return to testing if ordered by the president to "level the playing field."
China has firmly rejected the allegations. A spokesperson for the Chinese embassy in Washington described them as "entirely unfounded" and an attempt "to fabricate excuses for resuming" U.S. nuclear testing. Beijing's Foreign Ministry has repeatedly called the claims "completely groundless" or "outright lies," reaffirming its commitment to a moratorium on nuclear explosive testing since its last declared test in 1996. China like the US has signed but not ratified the Comprehensive Nuclear-Test-Ban Treaty (CTBT).
Independent verification remains elusive. The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) has stated that available data is insufficient to confirm a nuclear explosion, noting the detection of two very small seismic events spaced 12 seconds apart but lacking conclusive signatures. Ben Dando of NORSAR, a Norwegian seismic monitoring group, acknowledged explosion-like wave ratios but highlighted limitations: the weak signal was recorded at only one station, leaving open the possibility of a natural event.
Satellite imagery analyses, including from the Center for Strategic and International Studies (CSIS), have found no unusual activity at Lop Nur around the date in question, offering no conclusive support for or against the U.S. claims.
The allegations underscore broader concerns about China's rapid nuclear arsenal expansion and reluctance to join multilateral arms control talks. U.S. officials argue such activities threaten global stability, while critics caution that unverified accusations could escalate tensions without firm evidence.