State ACN Bureau

I'm honored to serve as Assistant Secretary for Arms Control and Nonproliferation, and grateful to @POTUS and @SecRubio for their confidence. Alongside the talented professionals of the ACN bureau, we will execute @POTUS 's mission of making America safer, stronger, and more prosperous. Stay tuned for updates on our efforts!

Pleased to meet with @iaeaorg Director General @rafaelmgrossi to reinforce the importance of strong U.S.-IAEA relations enabling the advancement of our shared objectives on nuclear safety, security, safeguards, and the peaceful uses of nuclear science and technology. Photo credit: Dean Calma/IAEA

@UnderSecT @State_IO

Chargé d'Affaires a.i. Robert Ewing welcomed to Manila @StateACN Principal Deputy Assistant Secretary Ann Ganzer, whose visit underscores 🇺🇸 commitment to 🇵🇭 energy security, including efforts to ensure nuclear power is safe, secure, and safeguarded. #PartnersInProsperity

Honored to host Assistant Secretary Yeaw of the @StateACN Department’s Bureau of Arms Control, Nonproliferation, and Disarmament, where we discussed how our mission delivers for the American people every day, from stopping the spread of nuclear weapons to strengthening space cooperation that supports U.S. security and prosperity.    @UnderSecT @State_IO

A firsthand look at the U.S. innovative technologies provided through @StateACN and @NNSANews support to IAEA safeguards. Game-changing instruments deployed in the field to assist @iaeaorg inspectors monitor and verify peaceful nuclear activities.

I’m grateful to Chargé Solomon and his excellent @usunvie team for their work across a wide range of vital U.S. interests from the peaceful use of outer space to nuclear nonproliferation.

@HudsonInstitute @UnderSecT Thanks to @RLHeinrichs and the team at @Hudson for a great event today.

In Geneva, @UnderSecT announced that the US detected Chinese yield-producing nuclear tests. At Hudson, Assistant Secretary Yeaw (@StateACN) gives more details about this June 22, 2020, supercritical detonation:

Landmark announcements strengthen 🇺🇸🤝🇵🇭 civil nuclear partnership: @USTDA will fund a $2.7 million feasibility study to help @Meralco assess and deploy U.S.-designed small reactors and develop an implementation roadmap. #USPH80 #PartnersInProsperity (1/3)

On Tuesday, @RLHeinrichs will sit down with Assistant Secretary of State Christopher Yeaw for a conversation on arms control, nonproliferation, and deterrence in an era of complex nuclear threats. @StateACN Watch live at 10:00 a.m.: hudson.org/events/assista…

Thank you to FM Abdullatif bin Rashid Al-Zayani of Bahrain, a major non-NATO ally, for visiting last week to discuss our civil nuclear cooperation and mutual pursuit of peace, prosperity, and trust. Our work benefits our industries, our bilateral partnership, our two peoples, and the Gulf region.

As throughout our history, the United States has maintained a willingness to seek strategic stability and arms control arrangements that are verifiable, enforceable, and contribute to the security of the United States and her allies. What we are proposing is not talks for the sake of talks—with this effort, the United States is looking for meaningful progress based in concrete actions. (6/6)

This confluence of factors – serial Russian violations, growth of worldwide stockpiles, and flaws in New START’s design and implementation – gives the United States a clear imperative to call for a new architecture that addresses the threats of today, not those of a bygone era. (5/6)

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 yield producing nuclear test on June 22, 2020. (4/6)

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. (3/6)

…almost all of the U.S. deployed nuclear forces were subject to New START while only a fraction of Russia's much larger stockpile was…exactly zero Chinese nuclear weapons were covered by New START. @mfa_russia @MFA_CPC (2/6)

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. (1/6) @UN_Disarmament @usmissiongeneva @usunvie

On February 5, 2026, the New START Treaty expired. Negotiated at a different time to meet a different challenge, New START no longer serves its purpose. Our desire to reduce global nuclear threats is genuine, but we will not accept terms that harm the United States or ignore noncompliance in the pursuit of an agreement for agreement’s sake. We will set high standards for all potential nuclear peers. And we will always negotiate from a position of strength. Please see my full posting on Substack. statedept.substack.com/the-next-era-o…

We were glad to host a U.S.-led symposium in Prague this week with 40 partners from around the world. We discussed implementing Iran-related UN Security Council resolutions and reaffirmed our shared commitment to compliance and non-proliferation.