U.S. Alleges Covert Chinese Nuclear Test Amidst Escalating Arms Control Concerns

U.S. Accuses China of "Yield-Producing Nuclear Test" in 2020

The United States government has publicly accused China of conducting a "yield-producing nuclear test" in 2020 and preparing for further tests. This serious allegation comes amidst the recent expiration of the New Strategic Arms Reduction Treaty (New START) between the U.S. and Russia, escalating international dialogue on nuclear arms control and non-proliferation. China has forcefully denied the U.S. claims as "groundless."

Despite specific details provided by U.S. officials, the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) and independent experts have stated that their monitoring systems did not detect an event consistent with a nuclear test at the specified time.

The allegations intensify discussions around nuclear arms control, testing moratoriums, and the non-proliferation framework, at a time when the last remaining U.S.-Russia nuclear arms treaty has expired.

Specifics of the U.S. Claim

On February 6, 2026, Thomas DiNanno, U.S. Under Secretary of State for Arms Control and International Security, presented evidence at the Conference on Disarmament in Geneva. He stated that the U.S. government possesses evidence of China conducting nuclear explosive tests, including at least one "yield-producing nuclear test" on June 22, 2020. DiNanno further claimed that China sought to conceal these activities, which involve preparing for tests with designated yields in the hundreds of tons, by "obfuscating the nuclear explosions" and employing "decoupling" to decrease seismic monitoring effectiveness.

Christopher Yeaw, Assistant Secretary for Arms Control and Nonproliferation at the U.S. State Department, offered more specific information. He pointed to a magnitude 2.75 seismic event detected by a Kazakhstan station on June 22, 2020, which originated approximately 450 miles away at China's Lop Nur nuclear test site. Yeaw asserted that there was "very little possibility that it is anything other than an explosion, a singular explosion" and described it as "quite consistent with what you would expect from a nuclear explosive test," explicitly claiming it was "yield-producing."

Concerns regarding China's activities at Lop Nur were initially raised in a June 2020 U.S. State Department compliance report. The report cited "possible preparation to operate its Lop Nur test site year-round, its use of explosive containment chambers, extensive excavation activities at Lop Nur, and lack of transparency on its nuclear testing activities."

Conflicting Evidence and Expert Assessments

The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) and independent experts have not corroborated the U.S. assessment. Robert Floyd, Executive Secretary of the CTBTO, confirmed that the organization's International Monitoring System (IMS) did not detect any event consistent with the characteristics of a nuclear weapon test explosion on June 22, 2020. Subsequent detailed analyses by the CTBTO have not altered this determination.

The IMS is designed to detect nuclear test explosions with a yield equivalent to or greater than approximately 500 tonnes of TNT, and it found no such event.

Ben Dando, head of seismology and verification at NORSAR, noted that while seismic wave ratios for the event were consistent with an explosion, the weak signal and reliance on a single recording station presented limitations. He concluded that it remains possible the event was natural and that there is "no 'strong conclusive evidence'" of a nuclear test. Dando estimated a magnitude 2.75 event could correspond to tens of tons of TNT, but decoupling could conceal an explosion of hundreds of tons or even a kilotonne.

China's Forceful Denial

Following the U.S. allegations, Chinese Ambassador Shen Jian, Deputy Permanent Representative to the United Nations Office at Geneva, opposed the "false narratives," stating that the U.S. is "the culprit for the aggravation of the arms race."

Chinese Foreign Ministry spokesperson Lin Jian further stated that the U.S. accusation is "completely groundless" and accused the U.S. of "fabrication of pretexts for its own resumption of nuclear tests."

Global Nuclear Testing Context and Treaties

The U.S. allegations against China unfold within the delicate framework of global nuclear testing moratoriums and arms control treaties.

The CTBT, signed by 187 nations and ratified by 178, unequivocally prohibits all nuclear test explosions. Both the U.S. and China are signatories but have not ratified the treaty. They currently maintain self-imposed moratoriums on yield-producing nuclear testing, with the U.S. last conducting a critical-level test in 1992 and China in 1996. Russia ratified the CTBT in 2000 but withdrew in 2023, citing the U.S. failure to ratify. All 27 European Union member states have ratified the CTBT, consistently urging all nations, particularly the Annex 2 states (including China, Russia, and the U.S.), to ratify it.

Ratified by 190 countries in 1970, the NPT is a cornerstone of global security, designed to prevent the spread of nuclear weapons and encourage disarmament. European officials and observers have warned that resuming explosive nuclear weapons testing could lead to nuclear proliferation among non-nuclear countries and severely undermine the NPT.

The last full-scale nuclear test occurred in North Korea in 2017. As of the current period, this marks the longest time in human history without a nuclear test since 1945. The CTBT permits sub-critical testing, which involves exploding small quantities of weapons-grade plutonium without initiating a nuclear chain reaction. Nuclear powers currently maintain their arsenals through supercomputer simulations and sub-critical experiments. Arms control experts note that the CTBT does not explicitly define what constitutes an "explosion," leading to ambiguity in interpreting treaty compliance regarding small nuclear chain reactions.

China's Expanding Nuclear Arsenal

China is reportedly engaged in a significant expansion of its nuclear arsenal, encompassing both warheads and delivery systems. This includes new intercontinental ballistic missile silos and a system for launching a nuclear-capable hypersonic glide vehicle into orbit. U.S. government estimates place China's current warhead count near 600, projected to grow to 1,000 by 2030 and 1,500 by 2035.

For comparison, the United States and Russia are assessed to have approximately 4,000 warheads each, with the U.S. figure reportedly declining and Russia's growing. Potential reasons for China's interest in developing lower-yield nuclear weapons or testing new designs include requirements for limited warfare or new platforms like hypersonic weapons, or to counter U.S. missile defenses, though China has not publicly explained these changes.

The Future of Arms Control: New START Expiration and China's Role

The New START agreement, the last remaining nuclear arms control treaty between the U.S. and Russia, expired on February 5, 2026, after a five-year extension. Russia withdrew from New START in 2023 but reportedly maintained adherence to the deployed nuclear weapon limits of 1,550 for each side. Russian President Vladimir Putin has expressed interest in renegotiating the treaty, but White House responses have been described as unenthusiastic.

Under Secretary DiNanno stated that New START's limits are "no longer relevant in 2026" given China's expanding arsenal and Russia's unconstrained systems. Former President Donald Trump had advocated for a "new, improved, and modernized Treaty."

U.S. Secretary of State and acting National Security Advisor Marco Rubio stated that true arms control in the 21st century "is impossible to do something that doesn’t include China."

However, Chinese officials have consistently rejected calls to participate in new nuclear arms control negotiations.

International Opposition and U.S. Testing Considerations

The U.S. allegations against China inevitably raise questions about the future of U.S. nuclear testing policy. Former President Trump previously announced plans for new nuclear testing "on an equal basis" with China and Russia. While U.S. Secretary of Energy Chris Wright had previously downplayed the possibility of resuming American yield-producing nuclear tests, Assistant Secretary Yeaw noted that the Pentagon is considering adding more nuclear weapons to America's arsenal. DiNanno stated the U.S. government is committed to efforts to "restore responsible behavior when it comes to nuclear testing," without explicitly stating whether the U.S. intends to conduct its own testing.

International bodies and allies have voiced strong opposition to the resumption of nuclear testing. The European Union has warned that resuming explosive nuclear testing would be "unwise and destabilizing" and would erode international consensus against it. Italy has characterized such testing as a "grave threat to global security and peace." France and Great Britain, both nuclear-armed U.S. allies and NATO members that have ratified the CTBT, also express strong opposition to resuming explosive testing.

Satellite analysis indicates significant expansion and construction of new tunnels at historic nuclear test sites in the U.S. (Nevada), Russia (Novaya Zemlya), and China (Lop Nur) over the past five years. Arms control experts do not predict imminent explosive testing, but the lead time for conducting such tests has reportedly decreased from years to months. Observers suggest that a U.S. resumption of testing to modernize its weapons would contradict NPT principles and could have significant long-term international consequences.