US Accuses China of Covert 2020 Nuclear Test Amid New Arms Race Fears

Geneva, Switzerland – February 6, 2026 – In a dramatic escalation of nuclear tensions, the United States publicly accused China on Friday of conducting a secret nuclear test in 2020, a claim swiftly denied by Beijing and contradicted by international monitors. The allegation, delivered at the United Nations' Conference on Disarmament in Geneva, comes just one day after the expiration of the New START treaty – the last major nuclear arms control pact between the US and Russia. This marks the first time since the 1972 Strategic Arms Limitation Talks (SALT I) that the world's two largest nuclear powers will operate without verified limits on their deployed strategic arsenals.

Thomas DiNanno, the US Under Secretary of State for Arms Control and International Security, leveled the charge during a plenary session, framing it as evidence of China's "reckless" nuclear buildup. Speaking to an audience of diplomats from over 60 nations, DiNanno declared, "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." He pinpointed a specific date: June 22, 2020, when he alleged China detonated "one such yield-producing test" at its Lop Nur test site in Xinjiang province.

DiNanno went further, accusing the People's Liberation Army (PLA) of employing sophisticated evasion tactics. "China's military sought to conceal testing by obfuscating the nuclear explosions because it recognizes these tests violate test ban commitments," he said. The US official highlighted a technique called "decoupling," where an explosive device is detonated in a large underground cavity to muffle seismic waves, making detection harder for global monitoring networks. This method, DiNanno claimed, was designed to evade the International Monitoring System (IMS) operated by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO).

The accusations are rooted in a broader US intelligence assessment. Declassified reports from the Defense Intelligence Agency (DIA) suggest China has modernized its nuclear forces at an unprecedented pace since 2019, expanding silos, missile production, and submarine capabilities. Satellite imagery has revealed over 300 new ICBM silos in western China, fueling Pentagon estimates that Beijing's stockpile could surpass 1,000 operational warheads by 2030 – up from roughly 500 in 2024. Critics in Washington argue this expansion undermines global non-proliferation efforts, especially as China refuses to join trilateral talks with the US and Russia.

However, the US claim faced immediate pushback from the very organization tasked with verifying nuclear tests worldwide. Robert Floyd, Executive Secretary of the CTBTO, issued a rare public rebuttal during the same session. "The CTBTO's International Monitoring System did not detect any event consistent with the characteristics of a nuclear weapon test explosion at that time," Floyd stated. "Subsequent, more detailed analyses have not altered that determination." The IMS, comprising 337 facilities across 89 countries, uses seismic, hydroacoustic, infrasound, and radionuclide sensors to detect explosions as small as two kilotons – equivalent to 1,000 tons of TNT.

Floyd's statement underscores the IMS's track record: it successfully identified North Korea's six nuclear tests between 2006 and 2017, including a 250-kiloton device in 2017. Experts note that while decoupling can reduce seismic signals by a factor of 10 to 100, it doesn't eliminate telltale signatures like xenon isotopes from nuclear fission, which CTBTO's noble gas stations can detect for weeks. "If China conducted a test yielding hundreds of tons, as alleged, our network would likely have picked it up," said a CTBTO official speaking anonymously. US sources, however, insist their intelligence draws from human sources, signals intelligence, and advanced modeling beyond public seismic data.

China wasted no time in firing back. Ambassador Shen Jian, China's permanent representative to the Conference on Disarmament, labeled the accusations "false narratives and unfounded accusations concocted by certain forces to smear and vilify China." In a fiery response, Shen reaffirmed Beijing's moratorium on nuclear testing, first declared in 1996 after its 45th and final test. "We abide by our commitment to suspend nuclear testing," he said, accusing Washington of "hyping up China's nuclear arsenal expansion" to justify its own "nuclear hegemony."

A spokesperson for the Chinese embassy in Washington echoed this to Business Insider, emphasizing Beijing's defensive posture: "China is committed to peaceful development, follows a policy of 'no first use' of nuclear weapons, and pursues a nuclear strategy focused on self-defense." Chinese state media, including Global Times, amplified the rebuttal, portraying the US as a hypocrite for failing to ratify the Comprehensive Nuclear-Test-Ban Treaty (CTBT) despite signing it in 1996. Russia, which ratified the CTBT in 2000 but withdrew its ratification in November 2023 amid Ukraine tensions, has remained silent on the latest spat.

The timing of DiNanno's remarks is no coincidence. They coincide with the Trump administration's aggressive push for a new multilateral arms control framework to succeed New START, which capped US and Russian deployed strategic warheads at 1,550 each and limited delivery vehicles to 700. The treaty's collapse – after Russia suspended participation in 2023 and refused verification flights – leaves a dangerous void. "Today, the United States faces threats from multiple nuclear powers," DiNanno argued. "A bilateral treaty with only one nuclear power is simply inadequate in 2026 and going forward."

Under President Trump's second term, the US has proposed a "New New START" involving China, Russia, and potentially others like France and the UK. Proponents argue it must address hypersonic weapons, novel delivery systems, and emerging threats like fractional orbital bombardment systems (FOBS), which China tested in 2021. Yet China has rebuffed invitations, with Shen reiterating Friday that Beijing's arsenal "is not on the same scale as those of the United States or Russia." China's estimated 500 warheads pale against the US's 3,700 and Russia's 4,380, per the Federation of American Scientists.

Shen expressed "profound regret" over New START's demise and urged Washington to heed Moscow's recent offer to freeze limits unilaterally. Analysts see this as diplomatic posturing: China seeks parity in negotiations, demanding the US and Russia cut to 1,000 warheads each before Beijing joins. "China's strategy is to wait out the superpowers while building minimum deterrence," said Tong Zhao, a senior fellow at the Carnegie Endowment for International Peace. "Accusations like this only harden their resolve."

The broader context reveals a fraying non-proliferation regime. Neither the US nor China has ratified the CTBT, stalling its entry into force – it requires all 44 "nuclear-capable" states to approve. India, Pakistan, and Israel never signed, while North Korea withdrew. Meanwhile, Iran's uranium enrichment and Russia's tactical nuclear saber-rattling in Ukraine heighten global anxieties. US projections warn China's buildup could trigger an Asian arms race, prompting India and others to expand.

Experts are divided on the 2020 test claim. Proponents cite US intelligence's history of accuracy, like exposing North Korea's programs. Skeptics point to past false alarms, such as 1990s suspicions of Russian sub-kiloton tests debunked by the IMS. "Without shared data, this risks a credibility gap," said Daryl Kimball of the Arms Control Association.

As diplomats reconvene in Geneva next week, the world watches a precarious standoff. With no tests banned by enforceable treaty and arsenals growing, Friday's exchange signals not just accusation, but the dawn of unconstrained nuclear competition. For the first time in decades, the shadow of mutual assured destruction looms without the guardrails of verification.