U.S. Accuses China of Secretive Nuclear Test as Arms-Control Agreements Lapse

The Washington Post

12:12 JST, February 7, 2026

The United States’ top nuclear arms official on Friday accused China of carrying out an undisclosed nuclear detonation in 2020, arguing that recent secretive underground tests by China and Russia have given Washington reason to conduct “parallel steps” as a decades-long moratorium on nuclear testing among major powers is unraveling.

Thomas DiNanno, the undersecretary of state for arms control, told the Conference on Disarmament in Geneva on Friday that Beijing is preparing tests “with designated yields in the hundreds of tons” and has interfered with international seismic monitoring systems to mask prior detonations.

“Today, I can reveal that the U.S. government is aware that China has conducted nuclear explosive tests … China carried out one such yield-producing test on June 22, 2020,” DiNanno said, adding that Russia is assisting Beijing in developing the weapons-grade fissile material needed to fuel its nuclear arsenal.

DiNanno’s remarks offered fresh context to President Donald Trump’s announcement a day earlier that he would not seek to renew the New START accord, the last major nuclear arms control agreement between Washington and Moscow. In a Truth Social post, Trump said the U.S. would instead pursue a “new, improved, and modernized” pact. In December, Trump said he had ordered the U.S. to resume nuclear weapons testing “immediately” – something it has not done since 1992 – citing the need to match what he said are secretive tests by Russia and China.

“Serial Russian violations, growth of worldwide stockpiles and flaws in New START’s design and implementation gives the United States a clear imperative to call for a new architecture that addresses the threats of today, not those of a bygone era,” said DiNanno, who argued that “constraints” placed on the U.S. under the unilateral moratorium with Russia had fueled the rapid growth of China’s arsenal.

Russia, he noted, had successfully tested its 9M730 Burevestnik “Skyfall” cruise missile and Status-6 Poseidon “Doomsday” nuclear-armed unmanned underwater vehicle in “the last few months.” DiNanno did not elaborate on the evidence underpinning U.S. assessments of the alleged Chinese and Russian tests.

The Chinese embassy in Washington did not respond to a request for comment on the alleged 2020 test but said it adheres to a nuclear testing moratorium and a “no first use” policy on nuclear weapons.

Spokesman Liu Pengyu said China hopes the U.S. will honor its “commitment to a moratorium on nuclear testing, and take concrete actions to uphold the international nuclear disarmament and nonproliferation regime.” The Russian embassy did not respond to a request for comment.

DiNanno said the White House would push for a broader agreement extending beyond the bilateral agreement with Russia, signaling that Washington would seek to bring China and other nuclear states into the framework – while acknowledging that crafting such a pact would be difficult.

“We cannot promise this process will be quick or easy,” said DiNanno. “It will require the participation of more than just Russia at the negotiating table.”

Beijing has historically refused to join such a pact, arguing that its arsenal remains far smaller than those of the U.S. and Russia and that it will not enter negotiations until its stockpile approaches parity with other major powers. It has, however, publicly stated that it observes a voluntary moratorium on testing under the Comprehensive Nuclear-Test-Ban Treaty (CTBT), which it signed in 1996 but never ratified.

A Pentagon report released in December said China possesses just over 600 nuclear warheads and that while production slowed over the past year, it remains on track to field 1,000 by 2030. By comparison, Russia’s nuclear arsenal is roughly 4,300 warheads with the U.S. at around 3,700 as of January 2025, according to the Stockholm International Peace Research Institute’s latest annual assessment.

Efforts to bring China into a new agreement will be complicated by the near-total freeze in nuclear dialogue between Washington and Beijing in recent years, which has repeatedly been derailed by broader tensions. In 2024, China publicly suspended nuclear discussions with the United States in response to U.S. arms sales to Taiwan.

“Washington is putting increasing pressure on Beijing to clarify and constrain its historic nuclear buildup, a primary driver of the U.S. decision to let New START expire and regain the option to enhance U.S. capabilities,” said Tong Zhao, an expert on China’s nuclear weapons program at the Carnegie Endowment for International Peace, a Washington think tank.

“The unequivocal accusation by DiNanno that China has been conducting nuclear explosive tests – and using techniques to conceal them – is unprecedentedly specific and makes it difficult for Beijing to evade calls for clarification,” he added. “Washington’s primary concern is no longer Russia … by contrast, Beijing is perceived as having both the capability and the will to challenge U.S. military dominance.”

Analysis of government documents and satellite imagery indicates that key facilities underpinning China’s nuclear program are expanding rapidly as part of a broader military buildup. That includes a sweeping overhaul of a network of classified sites used to manufacture warhead components, including plutonium pits and the high explosives used to trigger nuclear detonation.

While DiNanno’s accusations mark the first public U.S. assessment that Beijing carried out a specific test, State Department and Pentagon reports previously said it is possible China has conducted low-yield nuclear tests at the secretive Lop Nur facility – the site of its first atomic bomb test in 1964. The State Department report said continued work at the site in 2020, along with China’s “lack of transparency on its nuclear testing activities,” had raised concerns about its adherence to the “zero-yield standard” of the United States and its allies.

Zero-yield – or subcritical – tests do not produce a self-sustaining nuclear chain reaction and therefore result in no measurable nuclear explosive yield. Low-yield nuclear tests – which are still banned under the CTBT – generate relatively small explosive outputs, often harder to detect, while high-yield tests produce far larger explosions intended to validate full warhead capability.

Two people familiar with U.S. government monitoring of the China’s nuclear sites, including one State Department official, said DiNanno’s claim about a 2020 test most likely refers to internal U.S. government reports of low-yield activity at Lop Nur that were circulated in the State Department and Pentagon that year. Both spoke on the condition of anonymity due to the sensitivity of the matter.

“It was suspected that China had conducted a nuclear test in the tunnel area around 2020, possible very low-yield prep at least,” said Renny Barbiarz, vice president at AllSource Analysis, who conducts regular geospatial analysis of the Lop Nur site.

Recent satellite imagery analysis by Barbiarz’s team shows the Lop Nur site has continued to expand rapidly in recent years, including new tunnel excavations that could be used to conduct low-yield tests, as well as larger boreholes that may be preparations for higher-yield nuclear detonations.