The global nuclear order entered a new and uncertain phase this month after the United States accused China of conducting a covert nuclear explosive test in June 2020, a claim Beijing has categorically denied. The allegation surfaced at the Conference on Disarmament in Geneva just one day after the expiration of the New START treaty between the United States and Russia, underscoring how fragile the international arms control architecture has become.
The charge, delivered by US Under Secretary of State for Arms Control Thomas DiNanno, has quickly evolved into more than a dispute over seismic data. It now sits at the intersection of collapsing treaties, shifting nuclear doctrines and a broader geopolitical struggle over whether the era of nuclear restraint is ending.
Speaking before diplomats in Geneva, DiNanno alleged that China conducted at least one “yield-producing” nuclear explosive test in June 2020 and employed a technique known as “decoupling” to reduce the seismic signals associated with underground detonations.
Decoupling involves detonating a nuclear device inside a large underground cavity. Instead of transmitting the full force of the explosion into surrounding rock, much of the energy is absorbed by compressing air within the cavity. This significantly reduces seismic waves, making the test appear smaller on monitoring networks. While decoupling can obscure the true yield of an explosion, experts note it cannot completely hide it.
DiNanno argued that the alleged test violated China’s commitments under its declared moratorium on nuclear explosive testing, even though the Comprehensive Nuclear-Test-Ban Treaty (CTBT) has not entered into force.
China swiftly rejected the accusation. Shen Jian, China’s envoy at the Conference on Disarmament, described the claim as “false narratives” designed to inflame tensions and justify US military expansion. He countered that Washington was fueling a new arms race while attempting to shift blame onto Beijing.
Complicating the matter further, the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), which operates a global network of seismic, hydroacoustic and radionuclide sensors, said its monitoring system detected no explosion consistent with the US allegation.
The dispute highlights a long-standing ambiguity in the global nuclear testing regime. The CTBT was opened for signature in 1996 and signed by both the United States and China. However, neither country has ratified the treaty, meaning it has not entered into force and remains legally nonbinding.
Despite that, both states—along with most nuclear-armed powers—have observed voluntary moratoria on nuclear explosive testing for decades. The United States has not conducted a full-scale nuclear explosive test since 1992. China’s last acknowledged test occurred in 1996.
This informal but widely respected moratorium has been one of the most significant achievements of the post–Cold War era. It created a strong global norm against explosive nuclear testing, reinforced by the CTBTO’s monitoring capabilities and widespread political stigma attached to any violation.
The US accusation now challenges that norm. If accurate, it would represent a serious breach of trust. If unproven, critics argue, it risks eroding the very taboo that has constrained nuclear competition for nearly three decades.
Perhaps the most intriguing aspect of the accusation is its timing.
If US intelligence detected a covert Chinese test in 2020, why make the allegation public only now? The delay raises questions about whether the disclosure reflects newly declassified evidence or a broader strategic calculation.
Tomas Nagy, writing in Reuters this month, suggested that Washington may have concluded that China is unlikely to join a new arms control framework in the near future. Publicizing the accusation could therefore serve as a way to apply political pressure or justify a policy shift.
Yet if the United States possessed compelling evidence in 2020, critics argue, it is difficult to explain why the issue remained muted for years. The delayed disclosure suggests that the accusation may be as much about shaping future policy as about revisiting past events.
The allegation came just as New START—the last remaining bilateral nuclear arms control treaty between the United States and Russia—expired. The treaty had limited deployed strategic warheads and delivery systems while mandating data exchanges and inspections. Its expiration leaves the world’s two largest nuclear powers without binding constraints for the first time since the early 1970s.
Against this backdrop, the US charge against China appears less like an isolated compliance dispute and more like a signal that the era of traditional arms control may be ending.
Adding to the uncertainty, US President Donald Trump in late 2025 ordered preparations to resume US nuclear testing “on an equal basis,” citing alleged testing by China and Russia. He did not clarify whether he was referring to explosive nuclear tests or to flight-testing of nuclear-capable missile systems.
The order marked the first time in decades that a US president publicly directed preparations for renewed nuclear explosive testing. Though no test has yet been conducted, the move signaled that Washington is reconsidering long-held assumptions about nuclear restraint.
Trump has also indicated interest in negotiating a broader arms control framework that would include China. Previous US administrations had sought to draw Beijing into trilateral negotiations with Russia, but China—whose arsenal is far smaller—has consistently resisted.
The current dispute may therefore serve multiple purposes: highlighting alleged Chinese noncompliance, building domestic political support for testing readiness and increasing leverage in future negotiations.
China’s nuclear arsenal is estimated to include roughly 600 warheads, according to open-source assessments—about one-tenth the size of US and Russian stockpiles. However, Beijing is expanding its arsenal at the fastest pace in its history, constructing new missile silos, deploying advanced mobile launchers and developing submarine-based deterrent capabilities.
For decades, China adhered to a “minimal deterrence” posture, maintaining a relatively small force designed to ensure retaliation after a nuclear attack. That posture appears to be evolving toward a more sophisticated and potentially first-strike-capable force.
From Beijing’s perspective, joining a framework like New START before reaching parity would lock in permanent inferiority unless Washington and Moscow were willing to make deep cuts. That scenario remains politically improbable.
Framing China as a covert violator of testing norms may therefore be less about confirming a past event and more about shaping the strategic narrative. It places pressure on Beijing to justify its modernization while strengthening arguments in Washington for maintaining or expanding US capabilities.
Even without explosive testing, both the United States and China possess advanced facilities for simulating nuclear weapons performance.
The US National Ignition Facility (NIF) at Lawrence Livermore National Laboratory uses high-powered lasers to replicate conditions inside nuclear explosions. Combined with sophisticated computer modeling and decades of historical test data, the facility allows US scientists to assess warhead reliability and develop new designs without detonating full-scale devices.
China is constructing a similar laser fusion facility in Mianyang, Sichuan province. While it may take years to reach capabilities comparable to NIF, the project signals Beijing’s commitment to advanced weapons research within a test-ban environment.
Russia, meanwhile, does not appear to possess an equivalent large-scale laser fusion facility, though it retains extensive historical test data and design expertise.
If the testing moratorium collapses, however, the strategic landscape could shift dramatically. According to reporting by David Sanger and William Broad in The New York Times, US officials are considering reopening missile tubes on submarines, deploying new theater-range nuclear weapons and preparing for underground nuclear tests for the first time since 1992.
Doreen Horschig, writing in an April 2025 report for the French Institute of International Relations (IFRI), argues that accusations of covert testing and threats to resume testing are increasingly used as strategic tools rather than purely compliance-driven measures.
During the post–Cold War period, the political cost of nuclear testing was high. The CTBT monitoring regime and global norms made explosive tests rare and controversial. As formal arms control mechanisms weaken, however, states may see value in signaling readiness to test as a way of demonstrating resolve.
Such signaling carries risks. Linking policy changes to alleged violations by others can erode the testing taboo, increase mistrust and encourage reciprocal actions. What begins as rhetorical escalation can quickly become operational reality.
Daryl Kimball and Xiaodon Liang of the Arms Control Association have similarly warned that making allegations without presenting verifiable evidence undermines credibility and weakens nonproliferation norms. They argue that concerns about low-yield testing are better addressed through ratification of the CTBT, enhanced inspections and confidence-building measures.
Replacing verification with accusation, they contend, risks triggering a chain reaction of testing that would destabilize global security.
Despite the bleak outlook, there are signs that transparency remains valued.
Axios reported this month that US and Russian officials reached an understanding in Abu Dhabi to continue observing certain New START transparency practices even after the treaty’s expiration. These include data exchanges and notifications designed to maintain predictability.
Such arrangements suggest that even in the absence of formal treaties, both sides recognize the stabilizing value of mutual visibility into each other’s nuclear forces.
The question is whether similar mechanisms can be extended to include China or whether mistrust will dominate.
Ultimately, the debate over a possible June 2020 Chinese test is about more than seismic readings. It reflects a broader transition in global nuclear politics.
For decades, arms control relied on legally binding treaties, verification regimes and incremental reductions in deployed warheads. Today, that framework is eroding under the weight of geopolitical rivalry and domestic political shifts.
The expiration of New START leaves no binding limits on the world’s two largest arsenals. The CTBT remains unratified by key states. Accusations of covert testing are becoming tools of strategic communication.
In this environment, the line between compliance dispute and policy justification blurs.
If the United States is using the allegation to build support for renewed testing, it risks weakening a norm that has constrained nuclear competition for a generation. If China did conduct a covert test, it would signal that even the informal moratorium is fraying.
Either scenario underscores a central truth: the stability of the nuclear order depends less on the absolute number of warheads than on transparency, predictability and mutual confidence.
Even small nuclear tests, if openly declared and monitored, could theoretically be stabilizing in a transparent framework. Conversely, secretive accusations and ambiguous signals can magnify suspicion and accelerate arms racing.
The current moment resembles a hinge in nuclear history.
One path leads toward renewed competition, with resumed testing, expanded arsenals and diminished transparency. The other would require rebuilding trust through updated agreements, confidence-building measures and perhaps a reimagined arms control architecture that reflects a multipolar nuclear world.
Whether the US accusation becomes a catalyst for negotiations or a prelude to escalation remains uncertain.
What is clear is that the global arms control system—once anchored by treaties like New START and sustained by the testing taboo—is under unprecedented strain. In that context, the dispute over a single alleged test in 2020 may prove less significant than what it reveals about the direction of nuclear politics in 2026.
As the world’s major powers reassess their doctrines and capabilities, the stakes extend far beyond Geneva conference halls. The erosion of norms that have restrained nuclear competition for decades could reshape strategic stability for a generation.
For now, the allegation stands contested, the evidence undisclosed and the future of arms control uncertain. What happens next will determine whether the global nuclear order adapts to new realities—or fractures under their weight.
