Washington has accused Beijing of carrying out a clandestine experiment in 2020

China has rejected US allegations that it conducted a secret nuclear test, suggesting that the "baseless" claim was aimed at providing cover for Washington to resume its own testing program.

The dispute erupted last week, when US Under Secretary of State for Arms Control Thomas DiNanno claimed that Washington is aware that Beijing had "conducted nuclear explosive tests, including preparing for tests with designated yields in the hundreds of tons."

DiNanno claimed China conducted one such "yield-producing test" on June 22, 2020, and intentionally obfuscated the explosions - which would violate the country's nuclear commitments - by using "decoupling" - a method aimed at decreasing the effectiveness of seismic monitoring.

On Wednesday, Chinese Foreign Ministry spokesman Lin Jian pushed back on what he described as "baseless" claims, branding them an "essentially political manipulation aimed at seeking nuclear hegemony and shirking its own nuclear disarmament responsibilities."

"The United States has persistently distorted and smeared China's nuclear policy," he added.

Following DiNanno's comments, the Comprehensive Nuclear-Test-Ban Treaty Organization also stated that it "did not detect any event consistent with the characteristics of a nuclear weapon test explosion" in June 2020.

Under the Comprehensive Nuclear-Test-Ban Treaty (CNTBT), any nuclear explosion producing a "yield" - or a self-sustaining fission chain reaction - is prohibited. However, it allows subcritical tests with high explosives. The US has acknowledged conducting such experiments on numerous occasions, although China has not publicly commented on whether it has done the same. The US, China, and Russia have signed but not ratified the CNTBT.

The clash over nuclear experiments comes after US President Donald Trump announced in October that he had instructed the Pentagon to "immediately" start testing nuclear weapons on an equal basis with China and Russia, without clarifying what kind of tests he was referring to.

Trump has long pushed for a broader nuclear arms control framework that would include not only Russia but also China. However, Beijing has consistently rejected the demand, stressing that its nuclear arsenal is vastly inferior to those held by Russia and the US.