Washington: The United States has accused China of conducting a “yield-producing nuclear test” in 2020 and warned that Washington will no longer remain at an “intolerable disadvantage” as President Donald Trump pushes for a new multilateral arms control agreement.

Assistant Secretary of State for Arms Control and Non-Proliferation Christopher Yeaw told a Washington audience on Wednesday (local time) that the US government is “aware that China conducted one such yield-producing nuclear test on June 22, 2020,” near the Lop Nur test site.

“We are aware of yield-producing nuclear explosive testing in China,” Yeaw said at the Hudson Institute. “China has used decoupling, a method to decrease the effectiveness of seismic monitoring to hide its activities from the world.”

He cited seismic data showing a “2.75 magnitude” reading at “09:18 Zulu, Greenwich Mean Time,” detected at a Kazakhstan monitoring station. “There is very little possibility, I would say, that it is anything but an explosion. A singular explosion,” he said.

Yeaw added that the exact yield could not be determined because of decoupling techniques. “What the yield was is impossible to tell,” he said. “That it was super critical, that it was yield producing, is pretty obvious from the seismic graphs.”

China has not publicly acknowledged such a test. Yeaw said Beijing has relied on “opacity, silence, obfuscation, and deflection.”

The remarks come days after the expiration of the New Strategic Arms Reduction Treaty, or New START. Yeaw called the treaty flawed because it “constrained the United States while allowing China to remain completely unconstrained.”

“Only two blocks out of six were captured by the treaty,” he said, referring to US and Russian intercontinental warheads. “That’s a problem. That’s a big problem.”

He described China’s nuclear buildup as “geometric” and said it was expanding “by leaps and bounds.” Quoting a former US commander, he said that the growth was “breathtaking and maybe even beyond breathtaking.”

Yeaw stressed that Article VI of the Nuclear Non-proliferation Treaty (NPT) obligates all nuclear-weapon states to pursue disarmament talks. “I don’t see anywhere in Article VI a special caveat or assignment to the United States and Russia for special responsibility in this matter,” he said.

President Trump, he said, wants “a better agreement” and is offering China an opportunity to join “multilateral strategic stability talks.” “America first arms control cannot and does not mean America only arms control,” he said.

On nuclear testing, Yeaw cited Trump’s pledge to return to testing on an “equal basis.” He clarified that this did not mean a return to large atmospheric tests. “Equal basis doesn’t mean we’re going back to Ivy Mike-style atmospheric testing,” he said.

He quoted former US Ambassador Robinson, who warned that if adversaries test at yields that cannot be detected while Washington maintains strict limits, the United States would face “an intolerable disadvantage.”

Asked whether Washington had raised the issue with Beijing and Moscow, Yeaw said, “They have received cables from us, yes.” He added that he hoped for “productive discussions” in Geneva and Vienna.

Yeaw also linked arms control to extended deterrence. “In extending deterrence to our allies… the United States is doing more for non-proliferation than frankly, almost any other tool,” he said.

New START, signed in 2010, capped deployed US and Russian strategic nuclear warheads and delivery systems. It expired after a five-year extension, amid worsening US-Russia ties over Ukraine and broader strategic tensions.

The NPT Review Conference is scheduled for April. Washington is expected to press all nuclear-weapon states, including China, to engage in what Yeaw called “good-faith negotiations toward disarmament,” as global concerns grow over renewed nuclear competition among major powers.