A senior United States official has disclosed fresh evidence pointing to an alleged underground nuclear test by China in June 2020, reigniting debates over nuclear non-proliferation.

Assistant Secretary of State Christopher Yeaw, speaking at the Hudson Institute in Washington, cited seismic data from a remote station in Kazakhstan detecting a magnitude 2.75 explosion at China's Lop Nor test site on 22 June 2020.

Yeaw, a nuclear engineering expert with a doctorate and prior experience in intelligence, dismissed alternative explanations. He analysed additional data post-event, concluding there was 'very little possibility' it was anything other than a singular nuclear explosion. The signal did not match mining blasts or earthquakes, aligning instead with patterns expected from a nuclear detonation.

The Comprehensive Test Ban Treaty Organisation (CTBTO) operates the PS23 seismic station in Kazakhstan as part of its global monitoring network. This system spans the planet to detect clandestine tests. However, CTBTO Executive Secretary Robert Floyd noted two small seismic events, 12 seconds apart, far below the 500-tonne TNT threshold for confident identification.

China vehemently denies the claims. Embassy spokesperson Liu Pengyu labelled them 'entirely unfounded,' accusing the US of fabricating pretexts to resume its own testing program. He framed it as 'political manipulation' to evade disarmament duties and pursue 'nuclear hegemony.'

This revelation comes amid heightened tensions following the expiry of the New START treaty on 5 February. US President Donald Trump urges a trilateral pact with China and Russia, but Beijing resists, citing its modest arsenal—estimated at over 600 warheads by the Pentagon, projected to exceed 1,000 by 2030—compared to American and Russian stockpiles.

China's last acknowledged underground test occurred in 1996, adhering informally to the 1996 Comprehensive Nuclear-Test-Ban Treaty (CTBT), which it signed but has not ratified. The US, similarly unratified, halted tests in 1992, shifting to simulations and supercomputers under a multibillion-dollar Stockpile Stewardship Program.

Yeaw suggested China employed 'decoupling,' detonating the device in a vast underground cavity to muffle shockwaves and evade detection. This technique, known since Cold War experiments, reduces seismic signatures, complicating verification—a persistent challenge in arms control.

The CTBTO's 337-facility network excels at pinpointing explosions above certain yields but struggles with low-yield or masked events. Historical ambiguities abound: the 1979 Vela Incident, a suspected South African-Israeli test, evaded clear confirmation despite US suspicions.

Geopolitically, this fuels fears of a nuclear arms race. New START's lapse removes bilateral caps on US-Russian deployed warheads, while China's expansion—bolstered by silo fields and hypersonic missiles—prompts calls for inclusive talks. Yet Beijing insists on parity before negotiations.

The Lop Nor site, in Xinjiang's remote Tarim Basin, has hosted over 45 Chinese tests since 1964. Recent satellite imagery reveals silo construction, aligning with Pentagon assessments of a nuclear build-up to deter perceived US encirclement.

US allegations echo earlier claims at a Vienna conference this month, underscoring intelligence divergences. While CTBTO data lacks conclusiveness, Yeaw's analysis leverages classified refinements, highlighting tensions between public monitoring and national assessments.

For global stability, this underscores the CTBT's fragility—170 signatories, 187 total, yet key holdouts persist. Ratification by the US, China, India, Pakistan, Egypt, Iran, Israel, and North Korea remains elusive, weakening enforcement.

Amid these developments, Trump's trilateral overture faces scepticism. China views its forces as minimally deterrent, rejecting caps that freeze disadvantages. Russia, post-New START, signals potential parity breaches, escalating risks.

Verification remains pivotal. Advances in radionuclide sampling, hydroacoustics, and infrasound bolster CTBTO capabilities, yet low-yield tests like the alleged 2020 event test limits. International inspectors crave on-site access, barred under current regimes.

This episode strains the non-proliferation architecture, from the Nuclear Non-Proliferation Treaty to bilateral pacts. As nuclear modernisations accelerate—US Columbia-class submarines, Russian Sarmat missiles, Chinese DF-41 ICBMs—the spectre of miscalculation looms.

Stakeholders urge dialogue. The UN Secretary-General and IAEA chief advocate CTBT entry-into-force, while think tanks like Hudson warn of proliferation cascades if suspicions fester unchecked. Ultimately, resolving such claims demands transparency. Absent it, accusations risk eroding trust, propelling an era of unchecked expansion in the world's most destructive arsenal.

Reuters