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US sheds light on its allegation of Chinese nuclear test and urges nations to push for disarmament

FILE - Christopher Yeaw, center, arrives to a Senate Foreign Relations Committee confirmation hearing on his nomination to be an assistant Secretary of State, Nov. 19, 2025, on Capitol Hill in Washington. (AP Photo/Julia Demaree Nikhinson, File) (Julia Demaree Nikhinson, Copyright 2025 The Associated Press. All rights reserved.)

GENEVA – A U.S. official focusing on arms control on Monday provided what he called new, declassified details of a Chinese underground nuclear test nearly six years ago and urged countries to press China and Russia to do more on nuclear disarmament.

Christopher Yeaw, assistant secretary of state for the bureau of arms control and nonproliferation, spoke to a U.N.-backed body after the last nuclear arms pact between the United States and Russia expired this month. That has ended limits on the arsenals of the world’s biggest nuclear powers and raised concerns about a possible new arms race.

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Yeaw called for greater transparency from China and pointed to some shortcomings of the New START treaty, such as that it didn't address Russia's large arsenal of nonstrategic nuclear weapons — which counts up to 2,000 warheads.

ā€œBut perhaps its greatest flaw was that New START did not account for the unprecedented, deliberate, rapid and opaque nuclear weapons buildup by China,ā€ he told the U.N.-backed Conference on Disarmament.

Yeaw said Beijing ā€œhas deliberately, and without constraint, massively expanded its nuclear arsenalā€ despite its assurances to the contrary. He lamented a lack of transparency about China's ā€œendpointā€ or goals.

ā€œWe believe China may achieve parity within the next four or five years,ā€ he said.

Beijing has balked at any restrictions on its smaller but growing nuclear arsenal and denies carrying out such a nuclear test.

Details about alleged Chinese nuclear test in 2020

Yeaw led a U.S. delegation that met Monday with a Russian delegation and on Tuesday with Chinese and other delegations in Geneva, the State Department said. U.S. officials have already held repeated meetings with partners, including nuclear-armed France and Britain.

In his speech, Yeaw cited an explosion detected at the Lop Nur underground site in western China as a magnitude 2.75 seismic event on June 22, 2020, based on information collected from an international monitoring system station in neighboring Kazakhstan.

ā€œIt was a probable explosion based upon comparisons between historic explosions and earthquakes,ā€ he said. ā€œThe seismic signals were indicative of a single fire explosion, not typical of mining explosions.ā€

Yeaw said China has made it ā€œdifficultā€ for the international community to monitor its testing activities and that during talks, it rejected allowing seismic testing stations to be put at a comparable distance to Lop Nur that the U.S. allows near its test site in Nevada.

China rejects accusations

China's ambassador to the conference said Monday that Beijing ā€œresolutely rejects the unfounded accusationsā€ by the U.S. and lashed out at ā€œcontinued distortion and smearing of China’s nuclear policy by certain countries.ā€

ā€œThe U.S. accusation that China conducted a nuclear explosion test is completely unfounded and is merely a pretext for resuming its own nuclear testing,ā€ Ambassador Jian Shen said. ā€œThe U.S.’s practice of smearing other countries to evade international arms control obligations seriously damages its own international standing.ā€

If China conducted yield-producing nuclear explosive tests, it would severely tarnish its reputation as a responsible nuclear power, said Tong Zhao, a senior fellow focused on nuclear policy and China at the Carnegie Endowment for International Peace in Washington.

Some in the U.S. could cite that as justification for testing weapons again.

ā€œThere are American nuclear weapon scientists who genuinely think, no matter what other countries do, that the U.S. needs to resume nuclear testing simply to ensure its own arsenal would be reliable in the long run,ā€ Zhao said.

President Donald Trump in October pointed to U.S. intentions to resume nuclear tests for the first time since 1992, but Energy Secretary Chris Wright later said such tests would not include nuclear explosions.

Yeaw, speaking last week at the Hudson Institute, a think tank in Washington, pointed to Trump’s previous comments by saying the U.S. will return to testing on an ā€œequal basis.ā€ He said that doesn’t mean ā€œIvy Mike-style atmospheric testingā€ but ā€œpresumes a response to a prior standard. Look no further than China or Russia for that standard.ā€

In his first term, Trump tried and failed to push for a three-way nuclear pact involving China.

Just after the New START pact expired, Secretary of State Marco Rubio said the U.S. was ā€œpursuing all avenuesā€ to fulfill Trump’s ā€œdesire for a world with fewer of these awful weaponsā€ but insisted Washington would not stand by while Russia and China expand their nuclear forces.

ā€œSince 2020, China has increased its nuclear weapons stockpile from the low 200s to more than 600 and is on pace to have more than 1,000 warheads by 2030,ā€ Rubio wrote on Substack this month.

US presses other countries to get involved

The U.S. has expressed a willingness to pursue multiple diplomatic avenues over the issue — whether bilateral, in a small group of countries or in broader multilateral talks.

ā€œWe are looking to all of you to help encourage nuclear-weapon states like China and Russia to engage meaningfully in a multilateral process,ā€ Yeaw told the conference, which brings together some 65 countries on issues like nuclear, biological and chemical weapons.

Shen said China has consistently supported the goals of the Comprehensive Nuclear Test Ban Treaty, ā€œalways adheredā€ to the commitments of the five nuclear weapons states to suspend nuclear testing and ā€œneverā€ engaged in activities that violate the treaty.

He also suggested Beijing, which has been on a vigorous military buildup in recent years, still has fewer nuclear weapons than the U.S. or Russia and said it was ā€œunfair, unreasonable and unfeasibleā€ to demand China engage in three-way nuclear arms control talks.

ā€œChina’s nuclear arsenal is not on the same scale as the country with the largest nuclear arsenal, and the strategic security environment faced by China’s nuclear policy is completely different from that of the U.S.,ā€ Shen said.

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Associated Press writers Didi Tang and Ben Finley in Washington contributed to this report.