US Accuses China of Cheating on Nuclear Test Ban: 'Decoupling' Technique Used to Hide Explosion From the World

Did China pull off one of the most sophisticated concealed nuclear tests in history? Or is the US building a case to restart its own testing programme?

Washington says Beijing secretly detonated a nuclear device at its Lop Nur test site on 22 June 2020. The method allegedly used: 'decoupling' — setting off an explosion inside a massive underground cavity to dampen seismic signals. The problem? The global nuclear watchdog says it detected nothing consistent with a nuclear test that day.

The US Case

The accusation came from Under Secretary of State Thomas DiNanno at a UN disarmament conference in Geneva on 6 February 2026.

'I can reveal that the US government is aware that China has conducted nuclear explosive tests, including preparing for tests with designated yields in the hundreds of tons,' DiNanno said, NPR reported. 'China has used decoupling — a method to decrease the effectiveness of seismic monitoring — to hide its activities from the world.'

Days later, Assistant Secretary of State Christopher Yeaw provided more details at the Hudson Institute. A monitoring station in Kazakhstan picked up a magnitude 2.75 seismic event roughly 450 miles from Lop Nur on that June 2020 date.

'There is very little possibility that it is anything other than an explosion, a singular explosion,' Yeaw said, according to Newsweek.

What the Watchdog Actually Found

Here's where it gets tricky.

The Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO) confirmed its monitoring station recorded 'two very small seismic events, 12 seconds apart' on 22 June 2020. But Executive Secretary Robert Floyd was blunt: 'With this data alone, it is not possible to assess the cause of these events with confidence.'

The CTBTO's system can detect nuclear explosions with yields of approximately 500 tonnes of TNT or greater. These events fell far below that threshold.

A Centre for Strategic and International Studies satellite analysis of the Lop Nur site 'did not provide any conclusive findings to support or disprove the recent US allegations.' The researchers noted that Lop Nur is vast — it's possible that testing occurred elsewhere on the site with no visible optical indicators.

Beijing Fires Back

China isn't staying quiet.

'The US accusation of Chinese nuclear explosive tests is completely groundless,' Foreign Ministry spokesperson Lin Jian said during a press conference. 'China opposes the US fabrication of pretexts for its own resumption of nuclear tests.'

Chinese Embassy spokesperson Liu Pengyu called the allegation 'entirely unfounded' and accused Washington of 'political manipulation aimed at pursuing nuclear hegemony.'

Why the Timing Matters

President Trump announced in October 2025 that the US would consider resuming nuclear testing 'on an equal basis' with other powers. That statement alarmed arms control experts worldwide.

The New START treaty, the last nuclear arms control agreement between the US and Russia, expired on 5 February 2026. No replacement exists. For the first time since 1972, no legally binding limits constrain the world's two largest nuclear stockpiles.

UN Secretary-General António Guterres called the expiration 'a grave moment for international peace and security.'

And China? Its arsenal has grown fast. Pentagon estimates put Beijing's stockpile at around 200-300 warheads in 2019-2020. Today, it exceeds 600. The projection: over 1,000 by 2030.

What Happens Next

Tong Zhao, a senior fellow at the Carnegie Endowment for International Peace, told NPR he takes the US claims seriously. The allegations appear 'consistent with the very active status of China's Lop Nur nuclear testing site over many years,' he said.

But not everyone agrees that the US should respond by testing. Daryl Kimball of the Arms Control Association warned that a US return to nuclear testing would be 'technically unnecessary' and could trigger other nations to follow.

Jeffrey Lewis of the Middlebury Institute calculated on X that a magnitude 2.7 event at Lop Nur would equal roughly 18 tons of yield, or 400-700 tons if fully decoupled. For context, the Nagasaki bomb was about 20,000 tons.

So did China cheat? The evidence remains disputed. What's certain: the guardrails that kept nuclear powers in check for decades are gone. And ordinary people, not diplomats or generals, will pay the price if this spirals into a new arms race.

The question that opened this article still hangs in the air. The answer may determine whether the world's longest period without a nuclear test continues — or ends.