Portraits of Iranian military generals and nuclear scientists killed in Israel's June 13, 2025, attack are displayed on a sign as a plume of heavy smoke and fire rise from an oil refinery in southern Tehran.

At least 14 nuclear scientists are believed to be among those killed in Israel’s Operation Rising Lion, launched on June 13, 2025, ostensibly to destroy or degrade Iran’s nuclear program and military capabilities.

Deliberately targeting scientists in this way aims to disrupt Iran’s knowledge base and continuity in nuclear expertise. Among those assassinated were Mohammad Mehdi Tehranchi, a theoretical physicist and head of Iran’s Islamic Azad University, and Fereydoun Abbasi-Davani, a nuclear engineer who led Iran’s Atomic Energy Organization.

Collectively, these experts in physics and engineering were potential successors to Mohsen Fakhrizadeh, widely regarded as the architect of the Iranian nuclear program, who was assassinated in a November 2020 attack many blame on Israel.

As two political scientists writing a book about state targeting of scientists as a counterproliferation tool, we understand well that nuclear scientists have been targeted since the nuclear age began. We have gathered data on nearly 100 instances of what we call “scientist targeting” from 1944 through 2025.

The most recent assassination campaign against Iranian scientists is different from many of the earlier episodes in a few key ways. Israel’s recent attack targeted multiple nuclear experts and took place simultaneously with military force to destroy Iran’s nuclear facilities, air defenses and energy infrastructure. Also, unlike previous covert operations, Israel immediately claimed responsibility for the assassinations.

But our research indicates that targeting scientists may not be effective for counterproliferation. While removing individual expertise may delay nuclear acquisition, targeting alone is unlikely to destroy a program outright and could even increase a country’s desire for nuclear weapons. Further, targeting scientists may trigger blowback given concerns regarding legality and morality.

A policy with a long history

Targeting nuclear scientists began during World War II when Allied and Soviet forces raced to capture Nazi scientists, degrade Adolf Hitler’s ability to build a nuclear bomb and use their expertise to advance the U.S. and Soviet nuclear programs.

In our data set, we classified “targeting” as cases in which scientists were captured, threatened, injured or killed as nations tried to prevent adversaries from acquiring weapons of mass destruction. Over time, at least four countries have targeted scientists working on nine national nuclear programs.

The United States and Israel have allegedly carried out the most attacks on nuclear scientists. But the United Kingdom and Soviet Union have also been behind such attacks.

Meanwhile, scientists working for the Egyptian, Iranian and Iraqi nuclear programs have been the most frequent targets since 1950. Since 2007 and prior to the current Israeli operation, 10 scientists involved in the Iranian nuclear program were killed in attacks. Other countries’ nationals have also been targeted: In 1980, Mossad, Israel’s intelligence service, allegedly bombed Italian engineer Mario Fiorelli’s home and his firm, SNIA Techint, as a warning to Europeans involved in the Iraqi nuclear project.

Given this history, the fact that Israel attacked Iran’s nuclear program is not itself surprising. Indeed, it has been a strategic goal of successive Israeli prime ministers to prevent Iran from acquiring nuclear weapons, and experts had been warning of the increased likelihood of an Israeli military operation since mid-2024, due to regional dynamics and Iranian nuclear development.

By then, the balance of power in the Middle East had changed dramatically. Israel systematically degraded the leadership and infrastructure of Iranian proxies Hamas and Hezbollah. It later destroyed Iranian air defenses around Tehran and near key nuclear installations. The subsequent fall of Syria’s Assad regime cost Tehran another long-standing ally. Together, these developments have significantly weakened Iran, leaving it vulnerable to external attack and stripped of its once-feared proxy network, which had been expected to retaliate on its behalf in the event of hostilities.

With its proxy “axis of resistance” defanged and conventional military capacity degraded, Iranian leadership may have thought that expanding its enrichment capability was its best bet going forward.

And in the months leading up to Israel’s recent attack, Iran expanded its nuclear production capacity, moving beyond 60% uranium enrichment, a technical step just short of weapons-grade material. During Donald Trump’s first term, the president withdrew the U.S. from a multilateral nonproliferation agreement aimed at curbing Iran’s nuclear program. After being reelected, Trump appeared to change tack by pursuing new diplomacy with Iran, but those talks have so far failed to deliver an agreement – and may be put on hold for the foreseeable future amid the war.

Most recently, the International Atomic Energy Agency board of governors declared Iran in non-compliance with its nuclear-nonproliferation obligations. In response, Iran announced it was further expanding its enrichment capacity by adding advanced centrifuge technology and a third enrichment site.

Even if the international community anticipated the broader attack on Iran, characteristics of the targeting itself are surprising. Historically, states have covertly targeted individual scientists. But the recent multiple-scientist attack occurred openly, with Israel taking responsibility, publicly indicating the attacks’ purpose. Further, while it is not new for a country to use multiple counter-proliferation tools against an adversary over time, that Israel is using both preventive military force against infrastructure and targeting scientists at once is atypical.

Additionally, such attacks against scientists are historically lower tech and low cost, with death or injury stemming from gunmen, car bombs or accidents. In fact, Abbasi – who was killed in the most recent attacks – survived a 2010 car bombing in Tehran. There are outliers, however, including the Fakhrizadeh assassination, which featured a remotely operated machine gun smuggled into Iranian territory.

Israel’s logic in going after scientists

Why target nuclear scientists?

In foreign policy, there are numerous tools available if one state aims to prevent another state from acquiring nuclear weapons. Alongside targeting scientists, there are sanctions, diplomacy, cyberattacks and military force.

Targeting scientists may remove critical scientific expertise and impose costs that increase the difficulty of building nuclear weapons. Proponents argue that targeting these experts may undermine a state’s efforts, deter it from continuing nuclear developments and signal to others the perils of supporting nuclear proliferation.

Countries that target scientists therefore believe that doing so is an effective way to degrade an adversary’s nuclear program. Indeed, the Israel Defense Forces described the most recent attacks as “a significant blow to the regime’s ability to acquire weapons of mass destruction.”

Despite Israel’s focus on scientists as sources of critical knowledge, there may be thousands more working inside Iran, calling into question the efficacy of targeting them. Further, there are legal, ethical and moral concerns over targeting scientists.

Moreover, it is a risky option that may fail to disrupt an enemy nuclear program while sparking public outrage and calls for retaliation. This is especially the case if scientists, often regarded as civilians, are elevated as martyrs.

Targeting campaigns may, as a result, reinforce domestic support for a government, which could then redouble efforts toward nuclear development.

Regardless of whether targeting scientists is an effective counter-proliferation tool, it has been around since the start of the nuclear age – and will likely persist as part of the foreign policy toolkit for states aiming to prevent proliferation. In the case of the current Israeli conflict with Iran and its targeting of nuclear scientists, we expect the tactic to continue for the duration of the war and beyond.

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A militarily degraded Iran may turn to asymmetrical warfare – raising risk of proxy and cyber attacks

Israel’s air assault on Iran has focused largely on degrading the Islamic Republic’s military and would-be nuclear capabilities.

In the space of several days, Israel has totally or partially destroyed at least two nuclear sites, destroyed numerous air defense capabilities in a number of cities and killed at least 14 nuclear scientists and several senior leaders of the Iranian Islamic Revolutionary Guard Corps.

The Israeli operation has compromised how Iran can wage conventional warfare – through the use of military hardware, missiles, drones and aircraft. It has also likely curtailed any progress Iranian scientists had made in enriching uranium to a weapons-level grade, at least in the short-term.

But conventional military weapons are only one tool in Tehran’s arsenal. As a researcher who studies how Iran partners with militant groups, I know Iran still has the means to target its enemies. Despite the degradation of its military capabilities, Iran can leverage proxies, criminal organizations abroad, and cyberattacks to hit Israeli, and possibly U.S., targets.

Forward deterrence doctrine

The Islamic Republic is well suited for asymmetric warfare, or conflict between two countries that have different conventional capabilities and that is below the threshold of conventional war.

It fits a central tenet of Iran’s forward deterrence policy. In short, the doctrine holds that Iran should target its adversaries before their threat reaches the country’s borders. As Supreme Leader Ali Khamenei said in 2019, Iran “must not limit ourselves within our own borders. It is our duty to recognize and confront threats that lie beyond our walls.”

The “forward deterrence” doctrine was seeded from the early days of Iran’s Islamic Republic after the 1979 revolution.

Notably, forward deterrence originated from a need to cultivate proxies to target Saddam Hussein during the brutal eight-year war Iran fought against Iraq in the 1980s. To that end, Iran raised, equipped and trained groups like the Badr Corps to support its fight against Hussein, and it continues to support the militia and its political arm to the present day.

In more recent years, Iran has cultivated violent non-state actors like terrorist and rebel groups as well as criminal gangs to target adversaries – both the U.S. and Israel, but also regional rival Saudi Arabia. These non-state groups are primarily coordinated through the Revolutionary Guard’s Quds Force, its extraterritorial missions arm founded in 1988.

Recent Israeli strikes have degraded both Iran’s conventional military capability and killed members of Revolutionary Guard leadership. Israel also allegedly hit a Quds Force nerve center in Tehran, and it’s unclear if its leader, Esmail Qaani, is dead.

Meanwhile, operations earlier in the Israel-Gaza conflict have diminished the ability for some of Tehran’s proxies – notably Hezbollah in Lebanon and Hamas in Gaza – to respond.

Yet Tehran’s overall capacity for asymmetric retaliation has not been completely diminished. While it’s unclear how large the Quds Force is, by its very nature, its operatives are spread throughout the region. As a hierarchical, bureaucratic organization, it likely has a robust succession plan.

And its existing programs, directives and operatives will remain in place to be deployed or activated.

Kidnappings and assassinations

Of primary concern to policymakers in Israel and Washington will be the potential targeting of U.S. and Israeli assets abroad through Iran’s use of criminal organizations and proxies, as well as via Quds Force and Ministry of Intelligence operatives deployed throughout the world.

Since the Islamic Republic’s inception, it has targeted perceived enemies and political dissidents in assassinations perpetrated by these proxies and government operatives. In 1980, a former Iranian diplomat turned dissident, Ali Akbar Tabatabai, was assassinated in Maryland by a purported Iranian intelligence-linked network, one of the first known Iranian-backed killings on U.S. soil. In 1991, the intelligence ministry was accused of orchestrating the assassination of former Iranian Prime Minister Shapour Bakhtiar in France, reflecting Tehran’s policy of eliminating opposition leaders in exile.

A more recent example is Masih Alinejad, a New-York based critic of Tehran’s treatment of women, who U.S. prosecutors say has been the target of numerous kidnapping and assassination plots involving both Iranian operatives and an Eastern European organized crime group hired by Tehran.

Iran also reportedly cooperates with criminal groups in Europe, working with them to surveil Israeli targets in France, Germany and the U.K.

U.S. nationals have also been targeted directly. Iranian intelligence operatives were said to be behind the abduction of former FBI agent Robert Levinson in March 2007, for example.

And in 2022, a member of Iran’s Quds Force was indicted in the U.S. for plotting to assassinate former National Security Advisor John Bolton.

The size and number of operatives abroad of both the Quds Force and the Ministry of Intelligence’s operatives are classified, but estimates put the Ministry of Intelligence at around 30,000 personnel and the Quds Force at anything from 10,000 to 21,000.

The contours of Iran’s proxy network

Regionally, a key aspect of Iran’s forward deterrence doctrine has centered on the so-called “Axis of Resistance,” which includes groups like Hamas, Hezbollah and the Houthis. These forces have targeted U.S. and Israeli interests abroad, including in a number of high-profile terrorist attacks.

Characterizing the Axis of Resistance as mere proxies of Iranian foreign policy oversimplifies matters. In reality, the Axis comprises a complex network of strategic partnerships with ideologically aligned but autonomous groups – each with its own agenda, local support base, and relationship with Tehran.

Since its inception in the early 1980s, Lebanon’s Hezbollah has been seen to be Iran’s most reliable proxy when attacking U.S. or Israeli targets. Hezbollah’s external operations arm, Islamic Jihad Organization, was thought to be responsible for the 1983 U.S. embassy and Marine barracks bombing in Beirut, which left over 300 dead, collectively.

Similarly, prosecutors in Argentina believe Iran sponsored and Hezbollah carried out the 1994 bombing of a Jewish community center in Buenos Aires which left 85 dead. Similar efforts have been disrupted in Azerbaijan, Bulgaria and Thailand.

While Hezbollah had amassed a large arsenal and regional strength over the last two decades, its capabilities have been severely hampered by recent Israeli efforts, which saw many of the group’s top brass killed. And it is notable that Hezbollah has not launched any strikes on Israel’s north in concert with Iran’s efforts to counter Israel’s most recent offensive.

Unlike Hezbollah – or Hamas – the Houthis in Yemen remain largely undiminished in regards to their offensive capabilities.

On June 13, the Houthis launched missiles against Israel in response to the attack on Iran.

The Houthis have the capability to severely disrupt shipping in the Red Sea and Strait of Hormuz – a crucial waterway for global shipping.

For months after October 2023, the Houthis targeted commercial ships in the Red Sea. These attacks drove up shipping costs and led to U.S. and other navies escorting ships, exchanging fire and finally a U.S.-led bombing of Houthis in late 2023 and early 2024.

Finally, Iran also has alliances with a series of smaller proxies in Iraq and Syria that could be deployed against U.S. diplomatic and military targets in the region. One such group was behind the deadly bombing of a U.S. military base in Jordan that killed three U.S. soldiers in January 2024.

Iran’s cyberwarfare options

Another potential avenue of retaliation for Iran is a cyberattack – conducted either directly or through a proxy group.

Cybersecurity firm Radware noted a reported 700% spike in malicious online activity in the two days following the launch of the recent Israel operation, which it blamed on Iranian state actors and pro-Iranian hacker groups.

Cyberoperations are embedded in Iran’s broader forward deterrence doctrine.

Over the years, Tehran has built up a network of hacking groups to conduct reconnaissance, disinformation, data theft, sabotage and influence operations. Meanwhile, Iran is increasingly integrating AI tools into its cyberarsenal – making operations more agile, effective and less costly. After the Oct. 7, 2023, attack by Hamas, for example, Iranian-backed cyberactors used AI tools to generate propaganda imagery aimed at influencing Israeli public sentiment.

Then, following Iran’s April 2024 drone strike on Israel, Iranian-backed cyberactors employed AI to create fabricated video clips and images falsely depicting rockets and subsequent explosions launched into the night. These visuals were shared via platforms like X and were aimed at amplifying fear among Israelis.

A new dimension in the conflict

As the conventional warfare between Israel and Iran continues to downgrade Tehran’s military capabilities, the risk of asymmetric retaliation grows.

And Iran’s network of operatives, proxies and cyber actors may be harder to hit than stationary launching sites and military headquarters. They remain active and capable, even amid military degradation and leadership losses.

The more Tehran is pressured through direct strikes, the more likely it is to turn to these unconventional warfare tools. Although less visible, Iran’s unconventional warfare arsenal is a potentially dangerous dimension of this conflict.

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What are the nuclear contamination risks from Israel's attacks on Iran?

Israel's strikes on Iran's nuclear installations so far pose only limited risks of contamination, experts say. But they warn that any attack on the country's nuclear power station at Bushehr could cause a nuclear disaster.

Israel says it is determined to destroy Iran's nuclear capabilities in its military campaign, but that it also wants to avoid any nuclear disaster in a region that is home to tens of millions of people and produces much of the world's oil.

Fears of catastrophe rippled through the Gulf on Thursday when the Israeli military said it had struck a site in Bushehr on the Gulf coast - home to Iran's only nuclear power station - only to say later that the announcement was a mistake.

WHAT HAS ISRAEL HIT SO FAR?

Israel has announced attacks on nuclear sites in Natanz, Isfahan, Arak and Tehran itself. Israel says it aims to stop Iran building an atom bomb. Iran denies ever seeking one.

The international nuclear watchdog IAEA has reported damage to the uranium enrichment plant at Natanz, to the nuclear complex at Isfahan, including the Uranium Conversion Facility, and to centrifuge production facilities in Karaj and Tehran.

Israel has also attacked Arak, also known as Khondab.

The IAEA said Israeli military strikes hit the Khondab Heavy Water Research Reactor, which was under construction and had not begun operating, and damaged the nearby plant that makes heavy water. The IAEA said that it was not operational and contained no nuclear material, so there were no radiological effects.

In an update of its assessment on Friday, the IAEA said key buildings at the site were damaged. Heavy-water reactors can be used to produce plutonium which, like enriched uranium, can be used to make an atom bomb.

WHAT RISKS DO THESE STRIKES POSE?

Peter Bryant, a professor at the University of Liverpool in England who specialises in radiation protection science and nuclear energy policy, said he is not too concerned about fallout risks from the strikes so far.

He noted that the Arak site was not operational while the Natanz facility was underground and no release of radiation was reported. "The issue is controlling what has happened inside that facility, but nuclear facilities are designed for that," he said. "Uranium is only dangerous if it gets physically inhaled or ingested or gets into the body at low enrichments," he said.

Darya Dolzikova, a senior research fellow at London think tank RUSI, said attacks on facilities at the front end of the nuclear fuel cycle - the stages where uranium is prepared for use in a reactor - pose primarily chemical, not radiological risks.

At enrichment facilities, UF6, or uranium hexafluoride, is the concern. "When UF6 interacts with water vapour in the air, it produces harmful chemicals," she said.

The extent to which any material is dispersed would depend on factors including the weather, she added. "In low winds, much of the material can be expected to settle in the vicinity of the facility; in high winds, the material will travel farther, but is also likely to disperse more widely."

The risk of dispersal is lower for underground facilities.

Simon Bennett, who leads the civil safety and security unit at the University of Leicester in the UK, said risks to the environment were minimal if Israel hits subterranean facilities because you are "burying nuclear material in possibly thousands of tonnes of concrete, earth and rock".

WHAT ABOUT NUCLEAR REACTORS?

The major concern would be a strike on Iran's nuclear reactor at Bushehr.

Richard Wakeford, Honorary Professor of Epidemiology at the University of Manchester, said that while contamination from attacks on enrichment facilities would be "mainly a chemical problem" for the surrounding areas, extensive damage to large power reactors "is a different story".

Radioactive elements would be released either through a plume of volatile materials or into the sea, he added.

James Acton, co-director of the Nuclear Policy Program at the Carnegie Endowment for International Peace, said an attack on Bushehr "could cause an absolute radiological catastrophe", but that attacks on enrichment facilities were "unlikely to cause significant off-site consequences".

Before uranium goes into a nuclear reactor it is barely radioactive, he said. "The chemical form uranium hexafluoride is toxic ... but it actually doesn't tend to travel large distances and it's barely radioactive. So far the radiological consequences of Israel's attacks have been virtually nil," he added, while stating his opposition to Israel's campaign.

Bennett of the University of Leicester said it would be "foolhardy for the Israelis to attack" Bushehr because they could pierce the reactor, which would mean releasing radioactive material into the atmosphere.

WHY ARE GULF STATES ESPECIALLY WORRIED?

For Gulf states, the impact of any strike on Bushehr would be worsened by the potential contamination of Gulf waters, jeopardizing a critical source of desalinated potable water.

In the UAE, desalinated water accounts for more than 80% of drinking water, while Bahrain became fully reliant on desalinated water in 2016, with 100% of groundwater reserved for contingency plans, according to authorities.

Qatar is 100% dependent on desalinated water.

In Saudi Arabia, a much larger nation with a greater reserve of natural groundwater, about 50% of the water supply came from desalinated water as of 2023, according to the General Authority for Statistics.

While some Gulf states like Saudi Arabia, Oman and the United Arab Emirates have access to more than one sea to draw water from, countries like Qatar, Bahrain and Kuwait are crowded along the shoreline of the Gulf with no other coastline.

"If a natural disaster, oil spill, or even a targeted attack were to disrupt a desalination plant, hundreds of thousands could lose access to freshwater almost instantly," said Nidal Hilal, Professor of Engineering and Director of New York University Abu Dhabi's Water Research Center.

"Coastal desalination plants are especially vulnerable to regional hazards like oil spills and potential nuclear contamination," he said.