GENEVA, Switzerland — The United States has accused China of conducting secret nuclear tests, including activities designed to evade international monitoring, as it ramps up efforts for a new multilateral arms control agreement that would encompass Beijing alongside Washington and Moscow.
The allegations emerged during a United Nations Conference on Disarmament here on Friday, where Under Secretary of State for Arms Control and International Security Thomas DiNanno delivered pointed remarks. "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 stated, according to a transcript of his speech.
DiNanno further claimed that China employed a technique known as decoupling to reduce the detectability of these tests through seismic monitoring. He specified one instance on June 22, 2020, when much of the world was grappling with lockdowns due to the COVID-19 pandemic. "China has used decoupling — a method to decrease the effectiveness of seismic monitoring — to hide its activities from the world," DiNanno added in a post on X, the social media platform formerly known as Twitter.
These accusations come at a pivotal moment in global nuclear diplomacy. The 2010 New START treaty, which limited the deployment of strategic nuclear missiles and warheads between the US and Russia, expired on Thursday, marking the first time since the 1972 Strategic Arms Limitation Talks (SALT) agreement that the two powers face no binding constraints on their arsenals.
DiNanno emphasized the shifting landscape of nuclear threats. "Today, the United States faces threats from multiple nuclear powers. In short, a bilateral treaty with only one nuclear power is simply inappropriate in 2026 and going forward," he said. He warned that China is projected to expand its nuclear stockpile to more than 1,000 warheads by 2030, according to US intelligence assessments.
China's representative at the conference, Ambassador Shen Jian, pushed back against the US claims without directly refuting the specific allegations of testing. "The US continues in its statement to hype up the so-called China nuclear threat. China firmly opposes such false narratives … [The US] is the culprit for the aggravation of the arms race," Shen said in response.
Shen also expressed reluctance to engage in the proposed trilateral talks at this stage. "In this new era we hope the US will abandon Cold War thinking … and embrace common and cooperative security," he added, underscoring Beijing's position that Washington bears responsibility for escalating tensions.
The timing of the US disclosures aligns with broader geopolitical maneuvers. On the same day as DiNanno's speech, Russian, Ukrainian, and American delegations concluded two days of talks in Abu Dhabi, United Arab Emirates, focused on a potential peace settlement in Ukraine. Kremlin spokesman Dmitry Peskov commented on the discussions, noting that nuclear arms control was on the agenda.
"There is an understanding, and they talked about it in Abu Dhabi, that both parties will take responsible positions," Peskov told reporters Friday. "And both parties realize the need to start talks on the issue as soon as possible."
While Peskov's remarks referred primarily to the Ukraine negotiations, they highlighted a rare convergence of diplomatic channels where nuclear issues intersect with ongoing conflicts. The US has long viewed Russia's invasion of Ukraine, which began in February 2022, as a factor complicating arms control efforts, with Moscow suspending participation in New START inspections in 2023 amid the war.
Background on the New START treaty provides context for the current impasse. Signed by President Barack Obama and Russian President Dmitry Medvedev in 2010, the pact capped each side at 1,550 deployed strategic warheads and 700 deployed delivery vehicles. It was extended for five years in 2021 by Presidents Joe Biden and Vladimir Putin, but extensions beyond February 5, 2026, proved unfeasible amid deteriorating relations.
US officials have argued that excluding China from future agreements leaves a critical gap, given Beijing's rapid modernization of its nuclear forces. According to the US Defense Department's 2024 report on China's military, Beijing possessed about 500 operational nuclear warheads as of mid-2023, with projections indicating a tripling by the end of the decade. These developments, DiNanno suggested, necessitate a "broader arms control deal" to maintain strategic stability.
China, for its part, has maintained a policy of no-first-use of nuclear weapons and has historically resisted caps on its arsenal, citing the US and Russia's far larger stockpiles — estimated at around 3,700 and 4,380 warheads, respectively, by the Federation of American Scientists. Shen's comments echo Beijing's frequent assertions that it seeks parity only as a defensive measure.
International observers at the Geneva conference noted the challenges ahead. The Conference on Disarmament, established in 1979, has been stalled for years on key issues, including a fissile material cutoff treaty. DiNanno's revelations could further polarize discussions, with non-aligned nations like India and Pakistan — both nuclear powers — watching closely.
Looking forward, the US State Department indicated that Washington will continue pressing for inclusion of China in arms talks, potentially through informal channels or new frameworks. Meanwhile, the expiration of New START has prompted both the US and Russia to affirm compliance with the treaty's central limits voluntarily, at least for now, to avoid an unchecked arms race.
The accusations against China also revive debates over verification regimes. Seismic monitoring by the Comprehensive Nuclear-Test-Ban Treaty Organization has detected unusual activity at China's Lop Nur test site in the past, though Beijing insists all tests ceased in 1996. Independent experts, such as those from the Arms Control Association, have called for enhanced transparency to resolve discrepancies.
In Abu Dhabi, the trilateral talks on Ukraine touched on broader security concerns, including nuclear risks posed by the conflict. Ukrainian officials have repeatedly warned of radiation threats from damaged facilities like the Zaporizhzhia nuclear power plant, seized by Russian forces in 2022. Peskov's optimistic tone suggests some progress, but analysts remain cautious about breakthroughs.
As the world navigates this era of multipolar nuclear dynamics, the US push for a trilateral deal faces steep hurdles. China's insistence on equitable participation and Russia's entanglement in Ukraine complicate the path. Yet, with projections of global nuclear warheads exceeding 13,000, diplomats agree that renewed dialogue is essential to prevent escalation.
The Geneva conference continues through the week, with further sessions scheduled to address these tensions. For now, the US allegations stand as a stark reminder of the fragility of non-proliferation efforts in an increasingly contested geopolitical environment.