The allegation was raised days after the New START treaty expired, with Washington urging broader arms control that includes China as Beijing dismissed the charge as a false narrative
The United States has accused China of conducting a secret nuclear explosive test in 2020, renewing calls for a broader arms control treaty that would include China alongside Russia.
The allegation was made at the Conference on Disarmament in Geneva on Friday. This came a day after the New START treaty, the last pact limiting US and Russian strategic nuclear deployments, expired, leaving the two largest nuclear powers without binding constraints for the first time in more than five decades.
“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,” news agency Reuters reported Thomas DiNanno, US Under Secretary of State for Arms Control and International Security, as saying.
Notably, the alleged nuclear activity came just a week after the deadly Galwan Valley clashes in eastern Ladakh, where 20 Indian soldiers were killed in clashes with Chinese troops.
What did the US allege?
DiNanno said China had carried out one such “yield-producing test” on June 22, 2020, and had sought to conceal the activity using a technique known as “decoupling” to reduce the effectiveness of seismic monitoring.
“The Chinese military sought to conceal testing by obfuscating the nuclear explosions because it recognised these tests violate test ban commitments,” he said.
US President Donald Trump had earlier ordered the military to resume preparations for nuclear testing, saying other countries were doing so, though without naming them or providing details.
How did China reply?
China’s Ambassador for Disarmament, Shen Jian, did not directly address the specific allegation but strongly rejected Washington’s broader narrative.
“China notes that the US continues in its statement to hype up the so-called China nuclear threat. China firmly opposes such false narratives,” Shen told the conference. “It is the culprit for the aggravation of the arms race.”
In a separate statement this week, Shen said China followed a defensive nuclear strategy, maintained a “no first use” policy, and kept its arsenal at the minimum level required for national security, accusing the US of shifting responsibility for nuclear disarmament through “political manipulation”.
Monitoring body raises doubts
Robert Floyd, head of the Vienna-based body overseeing the Comprehensive Nuclear Test Ban Treaty, told Reuters that its international monitoring system “did not detect any event consistent with the characteristics of a nuclear weapon test explosion” at the time of the alleged Chinese test. He added that further analysis had not changed that assessment.
Both the US and China have signed but not ratified the treaty, which bans explosive nuclear tests. Russia ratified it but withdrew its ratification in 2023.
Why it matters
The accusations come at a critical juncture for global arms control. Trump wants a new agreement to replace New START and include China, which the US says is rapidly expanding its nuclear arsenal. Washington estimates China could have more than 1,000 nuclear warheads by 2030, a claim Beijing disputes, noting it has far fewer warheads than the US and Russia.
