The United States has accused China of conducting a covert nuclear test on June 22, 2020, just days after deadly clashes between Chinese and Indian forces in the Galwan Valley along the disputed Himalayan border. The allegation, made by U.S. Under Secretary of State for Arms Control and International Security Thomas DiNanno during a United Nations Disarmament Conference in Geneva, comes as the New START treaty, the last major arms control agreement between the U.S. and Russia, expired on February 5, 2026.
While Vladimir Putin proposed to extend the treaty for a year, Donald Trump rejected it, saying he wants a new disarmament treaty.
DiNanno revealed that the U.S. government knows that China carried out “nuclear explosive tests, including preparing for tests with designated yields in the hundreds of tons.” He said, “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.”
He specifically pointed to a “yield-producing test” on June 22, 2020, claiming Beijing employed a technique known as “decoupling,” which involves detonating explosives in large underground cavities to muffle seismic signals and evade international detection.
China has conducted nuclear explosive tests, including preparing for tests with designated yields in the hundreds of tons… China has used decoupling – a method to decrease the effectiveness of seismic monitoring – to hide its activities from the world. China conducted one such…
— Under Secretary of State Thomas G. DiNanno (@UnderSecT) February 6, 2026
This method, DiNanno argued, allowed China to obscure its activities in violation of global test ban commitments, even as the world grappled with the COVID-19 pandemic. The timing of the alleged test is significant for India, as it occurred one week after the June 15, 2020, skirmish in the Galwan Valley, where at least 20 Indian soldiers and an undisclosed number of Chinese troops were killed in hand-to-hand combat – the deadliest confrontation between the two nations in decades.
While U.S. officials did not explicitly link the nuclear test to the border conflict, it can not be ignored from an Indian point of view. The Galwan clashes, part of broader 2020-2021 India-China border tensions, involved aggressive troop movements and infrastructure buildups along the Line of Actual Control, exacerbating regional instability.
The Under Secretary of State stated this while defending the decision to not extend the New START treaty with Russia. He said “New START was signed in 2010 and its limits on warheads and launchers are no longer relevant in 2026 when one nuclear power is expanding its arsenal at a scale and pace not seen in over half a century and another continues to maintain and develop a vast range of nuclear systems unconstrained by New START’s terms,” referring to China and Russia.
He added that while almost all of the U.S. deployed nuclear forces were subject to New START, only a fraction of Russia’s much larger stockpile was under review, and “exactly zero Chinese nuclear weapons were covered by New START.” He further stated, “No longer constrained by the political-military circumstances of 2010 and the treaty they yielded and in response to the destabilizing behavior of these other countries, the United States can now finally take steps…to strengthen deterrence on behalf of the American people and our allies.”
