US Accuses China of Secret Nuclear Testing: A New Arms Race Shadow?

In a stark escalation of nuclear rhetoric, the United States publicly accused China of conducting covert nuclear explosive tests, breaching the long-standing global moratorium on such activities, the Comprehensive Nuclear-Test-Ban Treaty (CTBT)

On February 6, 2026, Under Secretary of State for Arms Control and International Security Thomas DiNanno addressed the Conference on Disarmament in Geneva, declaring that the U.S. government knows China has carried out "nuclear explosive tests," including preparations for blasts with yields in the hundreds of tons.

2020 nuclear test

He pinpointed one specific "yield-producing nuclear test" on June 22, 2020, and accused Beijing of deliberately concealing these events.The timing amplified the drama: the announcement came just one day after the New START treaty—the final major U.S.-Russia nuclear arms control pact—expired on February 5, 2026.

Without limits on deployed warheads or delivery systems between the world's two largest nuclear powers, DiNanno urged a new multilateral framework that includes China. He argued bilateral deals excluding Beijing are obsolete, given China's rapid arsenal growth. U.S. intelligence estimates suggest China could surpass 1,000 warheads by 2030, up from roughly 500 today, fueling concerns of an unchecked arms race.

Dramatic expansion of facilities

These claims center on China's Lop Nur test site in Xinjiang's remote desert, historically used for 45 nuclear detonations between 1964 and 1996. Recent satellite imagery from 2020–2024 shows dramatic expansions: new boreholes drilled into granite, horizontal tunnels excavated, upgraded infrastructure, access roads, support buildings, and possible explosive storage facilities.

Analysts describe a new "Eastern Probable Test Area" under construction—the first such development in decades—hinting at preparations for underground testing. Vehicle activity, electrical upgrades, and containment chambers have raised red flags, though much of this could support subcritical (zero-yield) experiments allowed under the de facto moratorium.

China rebuttal

China swiftly rejected the accusations as "false narratives" and "unfounded." Its disarmament ambassador, Shen Jian, emphasized Beijing's responsible nuclear posture, no-first-use policy, and adherence to its 1996 testing moratorium after signing (but not ratifying) the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Chinese officials countered by accusing the U.S. of hypocrisy, especially amid reports of the Trump administration exploring resumed U.S. testing for "parity." Beijing portrays the claims as threat inflation to justify American escalation.

Proof not published

To date, no publicly releasable evidence—seismic signatures, radionuclide detections, or declassified intelligence—has been shared to corroborate the specific 2020 test date or other claimed explosions. Earlier U.S. government reports dating back to 2019–2020 noted unusual activity at Lop Nur, including apparent blocking of data from nearby International Monitoring System stations, but those were framed more cautiously as "inconsistencies" rather than confirmed violations.

The International Monitoring System might detect larger blasts, yet smaller ones could evade notice.

Decoupling: Hiding nuclear blast seismic data

Central to the U.S. allegations is "decoupling," a sophisticated evasion technique designed to muffle seismic signals from underground explosions. In a fully decoupled test, the device detonates inside a large, pre-created cavity—often in salt domes or spacious voids—allowing energy to dissipate into gas or air rather than directly fracturing rock.

This dramatically reduces ground shock, slashing detectable seismic magnitude by factors of 70–100 or more, per historical experiments.The U.S. pioneered this with 1960s tests like Salmon (1966) and Sterling (1969) in Mississippi salt formations, achieving high decoupling for sub-kiloton yields.

The Soviets demonstrated partial decoupling at Azgir in 1976 with an 8–10 kiloton blast. For Lop Nur's granite and potential salt geology, even partial decoupling could obscure low-yield (hundreds of tons) events from global seismic arrays.

DiNanno explicitly cited this method, claiming China used it to "hide its activities from the world."

Critics highlight the challenges of creating such a test site. Excavating massive cavities risks collapse, venting, or detection via satellite/infrasound. High-frequency monitoring (up to 40 Hz) and dense networks could still penetrate partial decoupling for kiloton-range tests. Yet in an era of eroding trust and no binding treaty enforcement, decoupling epitomizes nuclear secrecy's enduring challenge—eroding verification confidence and heightening proliferation risks.

Immense stakes

The broader stakes are immense. New START's end removes caps for Russia and the US, while China's opacity and arsenal modernisation stoke paranoia although China was never a party to New START. Trump-era signals of potential U.S. test resumption could unravel the CTBT regime, inviting others to follow.

With Lop Nur's expansions visible from space yet motives opaque, this moment tests whether diplomacy can avert a new nuclear spiral—or if shadows at the test site foreshadow louder rumbles ahead.