Erin D. Dumbacher is a Stanton nuclear security senior fellow at the Council on Foreign Relations.
The U.S. military joined Israel’s bombing campaign against Iran on June 21, targeting nuclear sites at Natanz, Fordow, and Isfahan with bunker-buster bombs and cruise missiles. It remains unclear whether Iran retains a path to a nuclear weapon or if any of its enrichment capabilities or fissile material have gone underground. But Operation Midnight Hammer did not occur in a vacuum. It will likely have a chilling effect on nuclear nonproliferation efforts globally as states decide whether transparency is now a risk.
More on:
To avoid sending the message that states seeking nuclear weapons should retreat from the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) and hide their activities, the United States and Iran should reinforce the important role of the UN organization charged with nuclear oversight: the International Atomic Energy Agency (IAEA). There are still IAEA inspectors in Iran who are capable of onsite inspections and who would help verify the location of Iran’s fissile material and the state of the Iranian nuclear program. Unfortunately, Iran’s parliament took initial steps to suspend cooperation with the IAEA two days after the U.S. strikes.
Might to Make Right
On June 13, Israel began its bombing campaign to curtail the Iranian nuclear program after Iran enriched roughly four hundred kilograms of uranium to 60 percent—far beyond what is required for peaceful uses. The IAEA formally censured Iran for the first time in two decades the previous day for failing [PDF] to “provide the cooperation required” under its agreement with the agency. Iran is a party to the NPT, which requires states to be transparent about their nuclear programs and forbids them from acquiring nuclear weapons.
It was the international inspectors who estimated the fissile material Iran would need to produce a bomb in May and who estimated that Iran had not declared all the sites that had previously held nuclear material. Now, any other state considering whether to advance their nuclear program, even for civilian energy, could think twice about the diplomatic path Iran participated in for fear of inciting military retaliation.
After lengthy diplomatic efforts and difficult negotiations, Iran declared material and welcomed international inspectors for a time. But if a country that gave diplomacy a chance and has not raced to get the bomb can be attacked, why take part in the international nonproliferation system? Should states around the world expect military responses to their nuclear advances?
Precarious Incentives to Not Proliferate
The NPT and the associated safeguards and inspection regimes led by the IAEA form the core of the international nuclear nonproliferation regime. After states agreed in 1968 to create the two-tier structure of nuclear and non-nuclear weapons states within the NPT, the 186 countries without nuclear weapons committed to peaceful uses of nuclear material and technology. They agreed to declare any uranium enrichment or plutonium reprocessing activities to the IAEA and to sign comprehensive safeguards agreements.
More on:
In the 1990s, states recognized the limitations of these declarations, and 141 countries adopted an Additional Protocol in the ensuing years. These measures allow international inspectors to verify that the quantities of fissile material inside a country match its declarations. These two steps allow leaders and citizens around the world to have confidence that any nuclear material in a non-weapons state—such as low-enriched uranium for nuclear power plants or uranium used for health care—is not converted into materials for weapons. States chose to adopt these restrictions.
In exchange for complying with the NPT, countries joined the ranks of “normal nations,” avoided the “rogue state” label, and were considered members in good standing with the United Nations that could benefit from the energy, medical, and research advantages of nuclear technology. While it was always possible to renege or cheat, few countries pursued nuclear weapons—and those that did often withdrew from the treaty or never signed it at all.
Non-nuclear states that are hedging or sprinting to the bomb, using political scientist Vipin Narang’s framing, now could have an additional motive to be discreet about any weaponizing activities. A country with the technical means to weaponize nuclear material now could see downsides to allowing international inspectors to see and review their quantities and activities.
For decades, U.S. allies—including Germany, Japan, and South Korea—could have developed nuclear weapons, but U.S. policies, in part, have obviated their need to build a bomb. They have trusted that the United States would defend them with U.S. nuclear weapons in a worst-case scenario. If allies in Asia and Europe were to seek their own nuclear weapons, they would have few incentives to operate within the constraints of the NPT. Withdrawals from the NPT from member states historically in good standing would undermine the norm against proliferation, and more countries could just as easily follow.
Nuclear weapons, under the NPT, are permitted only by the initial five states that had weapons at the time of the treaty’s drafting: the United States, China, France, Russia, and the United Kingdom. Others that have gained nuclear weapons since—India, Israel, Pakistan, and North Korea—either withdrew from the treaty or did not sign on. Forty-seven states now have notable quantities of nuclear material, but it is those that do not comply with the NPT guardrails that most often make the news.
Iran’s Road to Nuclear Acceleration
Iran is one of those countries that made the news. It built up its uranium enrichment capacity and held more fissile materials than needed for energy or medical purposes, all while making existential threats to Israel.
Iran’s compliance with its NPT obligations and cooperation with the IAEA has varied over the years. From 2016 to 2019, under the terms of the Iran deal formally known as the Joint Comprehensive Plan of Action (JCPOA), the IAEA reported that Iran had allowed inspector access and complied with its obligations. But the United States retreated from the JCPOA in 2018, and Iran gradually stopped allowing IAEA access to sites, turned off monitoring technologies, and made it difficult to verify the specifics of its program.
A week before Israel launched its June 13 offensive, the IAEA calculated that Iran had over four hundred kilograms of uranium enriched to a 60 percent level. That is below the 90 percent threshold needed to build a weapon, but much higher than the 3–5 percent necessary for energy purposes. Their quantities of enriched uranium showed a marked increase from prior months at the same time that the country geared up for a new round of nuclear negotiations with the United States. (Iranian leaders were likely aware they would need leverage at hand.) In May, IAEA inspectors still had access [PDF] to some of Iran’s nuclear sites, including enrichment facilities, but it had been weeks since inspectors were able to review uranium stocks.
Agreeing to a resolution the United States raised, the IAEA Board of Governors declared on June 12 that Iran was not complying with its NPT obligations for the first time in two decades. Inspectors were still in the country when the Israeli bombing campaign began the next day, and they remain there now as Iran considers its future under the NPT.
While the damage to the Iranian nuclear sites from the U.S. strikes is still under assessment, the attack against Iran’s enrichment program could have put an end to Iran’s hospitality to international inspectors. Iranian leaders are voicing objections to the IAEA’s recent conduct and reviewing their participation in the NPT. There is precedent for such a move—North Korea withdrew from the NPT in 2003. (Despite this threat, Iran is still communicating with the IAEA, reporting to the agency that the Israeli strikes did not result in any offsite releases of radiation so far, though chemical and radiological consequences were reported within the facilities at Natanz.)
Global Effects
The potential regional and global effects of nuclear use are precisely why nations came together after the 1945 U.S. bombings of Hiroshima and Nagasaki to regulate the source material and facilities to make nuclear weapons. Any radiological release in Iran would be consequential for Iranians nearby and its neighboring countries. Europe learned the lesson from Chernobyl in 1986 that nuclear accidents or explosions do not abide by borders.
During an address before the UN Security Council on June 22, IAEA Director-General Rafael Grossi urged Iran to allow inspectors—who he called “guardians of the NPT”—in the country to “do their job.” In any future diplomacy with Iran, the United States should prioritize international, impartial inspections to both verify that Iran’s activities are peaceful and that the global standard of transparency for nuclear activities remains intact.
Diplomacy should be the path forward, as countries across the world are watching closely for what comes next. Leaders in non-nuclear weapon states could conclude that if international transparency into their nuclear programs is of no consequence to a permanent member of the UN Security Council like the United States, compliance with the fundamentals of the international nuclear nonproliferation regime brings risks they are not willing to take.
This work represents the views and opinions solely of the author. The Council on Foreign Relations is an independent, nonpartisan membership organization, think tank, and publisher, and takes no institutional positions on matters of policy.
The Nonproliferation Chilling Effect U.S. Strikes on Iran Nuclear Sites Could Cause
Countries without nuclear weapons could decide nuclear nonproliferation and transparency efforts that the world has taken for granted now pose more risk than reward.
June 27, 2025 4:19 pm (EST)
- Expert Brief
- CFR scholars provide expert analysis and commentary on international issues.
Erin D. Dumbacher is a Stanton nuclear security senior fellow at the Council on Foreign Relations.
The U.S. military joined Israel’s bombing campaign against Iran on June 21, targeting nuclear sites at Natanz, Fordow, and Isfahan with bunker-buster bombs and cruise missiles. It remains unclear whether Iran retains a path to a nuclear weapon or if any of its enrichment capabilities or fissile material have gone underground. But Operation Midnight Hammer did not occur in a vacuum. It will likely have a chilling effect on nuclear nonproliferation efforts globally as states decide whether transparency is now a risk.
More on:
To avoid sending the message that states seeking nuclear weapons should retreat from the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) and hide their activities, the United States and Iran should reinforce the important role of the UN organization charged with nuclear oversight: the International Atomic Energy Agency (IAEA). There are still IAEA inspectors in Iran who are capable of onsite inspections and who would help verify the location of Iran’s fissile material and the state of the Iranian nuclear program. Unfortunately, Iran’s parliament took initial steps to suspend cooperation with the IAEA two days after the U.S. strikes.
Might to Make Right
On June 13, Israel began its bombing campaign to curtail the Iranian nuclear program after Iran enriched roughly four hundred kilograms of uranium to 60 percent—far beyond what is required for peaceful uses. The IAEA formally censured Iran for the first time in two decades the previous day for failing [PDF] to “provide the cooperation required” under its agreement with the agency. Iran is a party to the NPT, which requires states to be transparent about their nuclear programs and forbids them from acquiring nuclear weapons.
It was the international inspectors who estimated the fissile material Iran would need to produce a bomb in May and who estimated that Iran had not declared all the sites that had previously held nuclear material. Now, any other state considering whether to advance their nuclear program, even for civilian energy, could think twice about the diplomatic path Iran participated in for fear of inciting military retaliation.
After lengthy diplomatic efforts and difficult negotiations, Iran declared material and welcomed international inspectors for a time. But if a country that gave diplomacy a chance and has not raced to get the bomb can be attacked, why take part in the international nonproliferation system? Should states around the world expect military responses to their nuclear advances?
Precarious Incentives to Not Proliferate
The NPT and the associated safeguards and inspection regimes led by the IAEA form the core of the international nuclear nonproliferation regime. After states agreed in 1968 to create the two-tier structure of nuclear and non-nuclear weapons states within the NPT, the 186 countries without nuclear weapons committed to peaceful uses of nuclear material and technology. They agreed to declare any uranium enrichment or plutonium reprocessing activities to the IAEA and to sign comprehensive safeguards agreements.
More on:
In the 1990s, states recognized the limitations of these declarations, and 141 countries adopted an Additional Protocol in the ensuing years. These measures allow international inspectors to verify that the quantities of fissile material inside a country match its declarations. These two steps allow leaders and citizens around the world to have confidence that any nuclear material in a non-weapons state—such as low-enriched uranium for nuclear power plants or uranium used for health care—is not converted into materials for weapons. States chose to adopt these restrictions.
In exchange for complying with the NPT, countries joined the ranks of “normal nations,” avoided the “rogue state” label, and were considered members in good standing with the United Nations that could benefit from the energy, medical, and research advantages of nuclear technology. While it was always possible to renege or cheat, few countries pursued nuclear weapons—and those that did often withdrew from the treaty or never signed it at all.
Non-nuclear states that are hedging or sprinting to the bomb, using political scientist Vipin Narang’s framing, now could have an additional motive to be discreet about any weaponizing activities. A country with the technical means to weaponize nuclear material now could see downsides to allowing international inspectors to see and review their quantities and activities.
For decades, U.S. allies—including Germany, Japan, and South Korea—could have developed nuclear weapons, but U.S. policies, in part, have obviated their need to build a bomb. They have trusted that the United States would defend them with U.S. nuclear weapons in a worst-case scenario. If allies in Asia and Europe were to seek their own nuclear weapons, they would have few incentives to operate within the constraints of the NPT. Withdrawals from the NPT from member states historically in good standing would undermine the norm against proliferation, and more countries could just as easily follow.
Nuclear weapons, under the NPT, are permitted only by the initial five states that had weapons at the time of the treaty’s drafting: the United States, China, France, Russia, and the United Kingdom. Others that have gained nuclear weapons since—India, Israel, Pakistan, and North Korea—either withdrew from the treaty or did not sign on. Forty-seven states now have notable quantities of nuclear material, but it is those that do not comply with the NPT guardrails that most often make the news.
Iran’s Road to Nuclear Acceleration
Iran is one of those countries that made the news. It built up its uranium enrichment capacity and held more fissile materials than needed for energy or medical purposes, all while making existential threats to Israel.
Iran’s compliance with its NPT obligations and cooperation with the IAEA has varied over the years. From 2016 to 2019, under the terms of the Iran deal formally known as the Joint Comprehensive Plan of Action (JCPOA), the IAEA reported that Iran had allowed inspector access and complied with its obligations. But the United States retreated from the JCPOA in 2018, and Iran gradually stopped allowing IAEA access to sites, turned off monitoring technologies, and made it difficult to verify the specifics of its program.
A week before Israel launched its June 13 offensive, the IAEA calculated that Iran had over four hundred kilograms of uranium enriched to a 60 percent level. That is below the 90 percent threshold needed to build a weapon, but much higher than the 3–5 percent necessary for energy purposes. Their quantities of enriched uranium showed a marked increase from prior months at the same time that the country geared up for a new round of nuclear negotiations with the United States. (Iranian leaders were likely aware they would need leverage at hand.) In May, IAEA inspectors still had access [PDF] to some of Iran’s nuclear sites, including enrichment facilities, but it had been weeks since inspectors were able to review uranium stocks.
Agreeing to a resolution the United States raised, the IAEA Board of Governors declared on June 12 that Iran was not complying with its NPT obligations for the first time in two decades. Inspectors were still in the country when the Israeli bombing campaign began the next day, and they remain there now as Iran considers its future under the NPT.
While the damage to the Iranian nuclear sites from the U.S. strikes is still under assessment, the attack against Iran’s enrichment program could have put an end to Iran’s hospitality to international inspectors. Iranian leaders are voicing objections to the IAEA’s recent conduct and reviewing their participation in the NPT. There is precedent for such a move—North Korea withdrew from the NPT in 2003. (Despite this threat, Iran is still communicating with the IAEA, reporting to the agency that the Israeli strikes did not result in any offsite releases of radiation so far, though chemical and radiological consequences were reported within the facilities at Natanz.)
Global Effects
The potential regional and global effects of nuclear use are precisely why nations came together after the 1945 U.S. bombings of Hiroshima and Nagasaki to regulate the source material and facilities to make nuclear weapons. Any radiological release in Iran would be consequential for Iranians nearby and its neighboring countries. Europe learned the lesson from Chernobyl in 1986 that nuclear accidents or explosions do not abide by borders.
During an address before the UN Security Council on June 22, IAEA Director-General Rafael Grossi urged Iran to allow inspectors—who he called “guardians of the NPT”—in the country to “do their job.” In any future diplomacy with Iran, the United States should prioritize international, impartial inspections to both verify that Iran’s activities are peaceful and that the global standard of transparency for nuclear activities remains intact.
Diplomacy should be the path forward, as countries across the world are watching closely for what comes next. Leaders in non-nuclear weapon states could conclude that if international transparency into their nuclear programs is of no consequence to a permanent member of the UN Security Council like the United States, compliance with the fundamentals of the international nuclear nonproliferation regime brings risks they are not willing to take.
This work represents the views and opinions solely of the author. The Council on Foreign Relations is an independent, nonpartisan membership organization, think tank, and publisher, and takes no institutional positions on matters of policy.
