The killing of Iranian nuclear scientists in U.S.-Israeli military strikes has raised fears that, if the regime destabilizes, weakened control over uranium stockpiles and the spread of nuclear expertise could increase proliferation risks.
While Iran can replace its lost personnel, experts say the lost expertise will be harder to rebuild and undisclosed sites in the country may also leave dangerous materials and knowledge vulnerable.
"Currently, the risk of nuclear terrorism or nuclear material moving to the black market remains low," said Kelsey Davenport, director of nonproliferation policy at the Arms Control Association.
"Non-state actors would face challenges in accessing enriched uranium, and it is unlikely they would have the infrastructure to enrich it to weapons-grade levels and convert it into the metallic form required for a warhead core," she said.
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"However, if the current Iranian government implodes or the conflict causes significant internal instability, there is an increased risk that nuclear materials will be stolen or diverted to undeclared sites."
"There is also a risk that Iranian nuclear scientists may be willing to sell their expertise to states or non-state actors seeking nuclear weapons," Davenport said in a new report.
Several senior figures in Iran’s nuclear and defense infrastructure have been killed over the past two years, coinciding with the campaign of U.S. and Israeli strikes on Iran’s nuclear facilities between 2025 and 2026.
Among them is Hossein Jabal Amelian, head of the Organization of Defensive Innovation and Research (SPND), who was killed in 2026 during Operation Rising Lion and Operation Epic Fury.
SPND is seen as the successor to Iran’s pre-2004 nuclear weapons program and plays a key role in new weaponization research.
Others killed in 2025 include Mohammad Mehdi Tehranchi, Akbar Motallebizadeh and Said Borji, all linked to weaponization work.
"The full impact of this campaign on Iran’s weaponization capabilities remains unclear," Jim Lamson, a senior research associate at the Center for Nonproliferation Studies, told Fox News Digital.
"There will be replacements of the managers and scientists, but the impact on the killed officials' experience and expertise will be hard to replace," the former CIA analyst said.
"Many key scientists involved in suspected weaponization work were killed in 2025 and 2026."
"Their successors may also fear being targeted in the future, whether by military strikes or assassination. That could affect their motivation and willingness to participate in any nuclear weapons program."
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Lamson also said many of those targeted were embedded in sensitive areas of Iran’s nuclear work, including the fuel cycle and weaponization.
"These scientists had expertise in areas of the nuclear fuel cycle of key concern for nuclear weapons, including the production of highly enriched uranium (HEU), which was Iran's main pathway for fissile material," he said.
"The scientists also had expertise in weaponization — that is, in key aspects of the design and production of nuclear explosive devices," Lamson added.
That said, U.S. and Israeli targeted strikes have also hit a network of sites tied to their work, creating extra obstacles for Iran’s program in the near term, he said.
"We have identified at least 11 weaponization-related sites that have been hit since 2024," Lamson said.
"These include SPND headquarters, a newly identified site called Min-Zadayi in northeast Tehran, SPND’s Taleghan and Sanjarian explosives testing sites, the Defense Ministry’s Shahid Meisami complex in western Tehran and several research universities."
These facilities were all involved in neutronics, explosives, metallurgy and nuclear physics — all tied to nuclear weapons development, he said.
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Despite the scale of the latest strikes, Iran retains enriched nuclear material, with President Donald Trump saying April 17 that the U.S. would work with Iran to recover "nuclear dust" — enriched uranium — from sites, adding that both countries would use heavy machinery to remove it.
The International Atomic Energy Agency also estimates Iran still holds more than 200 kilograms of uranium enriched to 60% at Esfahan—enough for roughly five weapons if further enriched.
Iranian Foreign Minister Seyed Abbas Araghchi also said it remains "under the rubble" of previous strikes and that Tehran has no plans to recover it.
"It is always possible that Iran has additional sites that were not known to Israel and the U.S.," Lamson said.
"We will have to wait to see how much these operations translate into a lasting strategic impact on Iran’s ability to produce nuclear weapons."
"It’s easier to identify the damage and death caused by the Israeli and U.S. strikes, and harder to assess their actual impact on Iran's capabilities and intentions to produce a nuclear weapon," Lamson clarified.
