US claims China ran a covert nuclear test days after Galwan clash with India; used ‘decoupling’ to hide it

US Under Secretary Thomas G DiNanno alleges Beijing conducted a covert, yield-producing nuclear test days after the 2020 India-China Galwan clash.

• US alleges China conducted covert nuclear test days after 2020 Galwan clash
• China accused of using "decoupling" to hide nuclear test from global monitoring
• Allegations may strain US-China ties and impact global arms control efforts

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The United States has alleged that China carried out a covert nuclear explosive test days after the deadly 2020 Galwan clash with India, a claim that sharpens scrutiny of Beijing’s nuclear activities and raises fresh questions over the future of global arms control.

US Under Secretary of State Thomas G DiNanno said China conducted a 'yield-producing' nuclear test on June 22, 2020, just a week after the Galwan skirmish began on June 15, when 20 Indian soldiers were killed in action along the Line of Actual Control.

Allegations of covert testing

In a post on X, DiNanno claimed China had conducted nuclear explosive tests involving yields in the “hundreds of tons” and employed techniques designed to conceal them from international monitoring.

“China has used decoupling – a method to decrease the effectiveness of seismic monitoring – to hide its activities from the world,” he wrote, alleging that the June 22 test was deliberately masked.

China has conducted nuclear explosive tests, including preparing for tests with designated yields in the hundreds of tons… China has used decoupling – a method to decrease the effectiveness of seismic monitoring – to hide its activities from the world. China conducted one such…

— Under Secretary of State Thomas G. DiNanno (@UnderSecT) February 6, 2026

Indian authorities had earlier stated that over 30 Chinese soldiers were also killed in the Galwan clash, though Beijing has never released official figures.

What is ‘decoupling’?

According to DiNanno, “decoupling” involves conducting a nuclear explosion in a way that dampens seismic signals, making detection by global monitoring systems more difficult. Such techniques, if proven, would challenge the effectiveness of international verification regimes designed to enforce nuclear test bans.

China has not responded publicly to the specific allegation.

DiNanno also used the allegation to argue for a rethink of global arms control frameworks, saying existing treaties no longer reflect current threats.

Referring to the New START treaty signed in 2010, he said nearly all US deployed nuclear forces were covered under its limits, while only a fraction of Russia’s larger arsenal fell within the agreement. China, he said, was not constrained by New START at all.

He argued that the political and military conditions that shaped the treaty in 2010 no longer apply in 2026, calling for a new nuclear architecture to strengthen deterrence.

Push for three-way nuclear talks

DiNanno’s remarks came as Washington presented a plan advocating three-way nuclear discussions involving the US, Russia and China after New START expired on Thursday. China has already rejected joining such disarmament negotiations “at this stage”.

Former US President Donald Trump had hinted at similar concerns last year, saying Washington could resume nuclear testing “on an equal basis” with Moscow and Beijing, without providing specifics.

The latest allegations are likely to add strain to US-China relations and inject fresh volatility into global non-proliferation efforts, particularly as arms control agreements face growing uncertainty.