By Jennifer Hansler, Kylie Atwood, CNN
(CNN) — The United States on Friday accused China of carrying out a secret nuclear test in 2020 as the Trump administration calls for a broader nuclear weapons agreement including both China and Russia.
The allegation comes a day after the last remaining nuclear arms control treaty between the US and Russia lapsed, leaving the world’s largest nuclear superpowers without limits on their arsenals for the first time in decades.
President Donald Trump and other top officials in his administration have made clear they will no longer abide by the limitations of the New START Treaty and instead have argued they need a new deal to address threats from Moscow and Beijing. And Trump last year called for the resumption of US nuclear weapons tests.
“Today, I can reveal that the U.S. Government is aware that China has conducted nuclear explosive tests, including preparing for tests with designated yields in the hundreds of tons,” Undersecretary of State for Arms Control and International Security Thomas DiNanno said in remarks at a global Disarmament Conference in Vienna Friday.
“China conducted one such yield producing nuclear test on June 22 of 2020,” he said, without providing further details. A former senior US official told CNN that information about China’s 2020 test had been declassified.
DiNanno accused the Chinese military of seeking “to conceal testing by obfuscating the nuclear explosions because it recognized these tests violate test ban commitments.”
“China has used decoupling – a method to decrease the effectiveness of seismic monitoring – to hide their activities from the world,” he said. According to experts, decoupling happens when a large cavern is dug to lessen the seismic activity from a nuclear explosion, making it harder to detect.
A top official from an organization that works to monitor for nuclear weapons tests worldwide said in a statement Friday that their system “did not detect any event consistent with the characteristics of a nuclear weapon test explosion” on June 22, 2020.
“Subsequent, more detailed analyses have not altered that determination,” said Rob Floyd, the executive secretary of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO).
Floyd said the organization’s International Monitoring System (IMS) “is capable of detecting nuclear test explosions with a yield equivalent to or greater than approximately 500 tonnes of TNT.” He noted it had detected “all six tests conducted and declared by” North Korea.
A yield below 500 tons, which the system would not be able to detect, “is roughly 3 percent of the yield of the explosion that devastated Hiroshima,” he said. Floyd noted that there are mechanisms provided by the Comprehensive Test Ban Treaty (CTBT), which bars “any nuclear weapon test explosion or any other nuclear explosion.” However, those mechanisms can only be used when the treaty enters into force.
Most of the world has signed onto and ratified the treaty. Although both the US and China signed, they have not ratified it and Russia withdrew its ratification in 2023. As such, the Treaty cannot enter into force.
The US and China in the past had said they adhere to a moratorium on nuclear testing, but last year, Trump called for US nuclear weapons testing to resume “on an equal basis.”
In his remarks on Friday, DiNanno suggested that the alleged Chinese testing had motivated Trump’s decree. He also said that “the annual US compliance report has previously assessed that Russia has failed to maintain its testing moratorium by conducting supercritical nuclear weapons tests.”
Asked about the allegation of secret nuclear testing, the spokesperson for the Chinese Embassy in Washington, DC, said China “ follows a policy