Beyond the Reactor

With Israel’s strikes against Iranian territory on June 13, 2025, the long-simmering confrontation between Israel and Iran has escalated into open hostilities, marking a dangerous new phase in their conflict. Under the codename “Operation Rising Lion”, Israel sought to prevent Iran from completing the development of a nuclear weapon. In the early hours of June 13, Israeli forces targeted, among other sites, the key uranium enrichment facility at Natanz, the Isfahan Nuclear Technology Center (INTC), as well as several Iranian Air Force bases. These strikes reportedly resulted in the deaths of senior military personnel as well nuclear scientists (here).

This post focuses on specific issues of the ius in bello relating to the potential protection of Iran’s nuclear program. The assessment is based on publicly available information, and while the conflict appears to have been settled, the picture is by no means complete. Many questions surrounding this conflict, such as jus ad bellum violations committed by Israel and the United States (see here, here, here and here) have already been discussed elsewhere. The same can be said for some facets of the ius in bello (here or here) or specific questions concerning, for example, air space violations or the consequences of disproportionate or unnecessary acts of self-defense (here). This post, instead, will examine to what extent uranium enrichment facilities, nuclear research centers, and their personnel, that Israel claims are linked to the development of nuclear weapons, are protected under international humanitarian law (IHL), and whether any specific or heightened protections apply to such targets in the conduct of hostilities.

Targeting Nuclear Scientists?

If it was not already applicable before, the application of IHL was triggered – at the latest – by the Israeli attacks on June 13, to which IHL applies under the so-called “first shot doctrine”. It must be observed that, since neither Iran nor Israel are state parties to the Additional Protocol (AP) I (although Iran has signed it), their relevant obligations stem mostly from Customary International Humanitarian Law (CIHL).

According to CIHL, civilians are generally protected from attacks, which may only be directed against military objectives such as combatants. This protection only ceases if and as long as a civilian is directly participating in hostilities (Rule 6 or Article 51(3) AP I). According to the ICRC’s Interpretive Guidance on the Notion of Direct Participation in Hostilities (ICRC Report DPH), scientists are only engaging in indirect, not direct, participation (p. 53). The United States, on the other hand, describe civilian scientists holding key positions in national weapon’s programs as “quasi-combatants” and potential legitimate targets (p. 6). Similarly, others propose that in a case-by-case assessment, factors such as the advancement stage of the weapons program and the individual scientist’s actual contribution to the research or its implementation (see Schmitt) may amount to a direct participation in hostilities. Compared to the overwhelming consensus rejecting the qualification of scientists as directly participating in hostilities across academic experts (see, ICRC Report DPH, p. 49), the U.S. position represents a minority view.

While in the past, scientists like Mohsen Fakhrizadeh, who has been the target of an Israeli attack in 2020, have conducted research as members of the armed forces or a similar formation (cf. Rule 5 or Article 50(1), 43 AP I), the same cannot be confirmed with the scientists killed now. Consequently, scientists engaged in nuclear research and development programs remain civilians under IHL and may not be targeted directly. As far as they have been targeted deliberately – as at least some scientists appear to have been – this constitutes a violation of the principle of distinction and amounts to a grave breach of IHL and a war crime. The deaths of the scientists would only be lawful under CIHL if they occurred incidentally during attacks on legitimate military objectives. This would first require Israel to demonstrate that the incidental loss of civilian life was not excessive in relation to the concrete and direct military advantage anticipated, and all feasible precautions were taken to avoid or minimize civilian harm. Crucially, however, this line of argument presupposes that the targeted sites qualified as lawful military objectives—an issue addressed in the following sections.

Targeting Nuclear Infrastructure?

For these facilities to constitute lawful targets under IHL, they must qualify as military objectives. CIHL – mirrored in Article 52(2) AP I – defines military objectives as “objects which by their nature, location, purpose or use make an effective contribution to military action and whose total or partial destruction, capture or neutralization, in the circumstances ruling at the time, offers a definite military advantage.” (ICRC, Rule 8). Any objective that is not military is regarded as civilian under custom (ICRC, Rule 9) and must not be attacked (ICRC, Rule 7). In cases of doubt, an objective is presumed to be civilian until proven otherwise (Rule 10).

While Iran maintains that its uranium enrichment program serves solely civilian purposes – namely, nuclear energy production – Israel and the International Atomic Energy Agency (IAEA) have raised concerns that the level of enrichment suggests potential military applications. What appears relatively certain at this stage is that enrichment sites in Natanz and Fordo as well as the Isfahan Nuclear Technology Center were targeted .

Given their character as research and enrichment sites not formally subordinated to military command structures, those should presumptively be regarded as civilian in nature. Only if these facilities make a sufficient contribution to Iran’s military capabilities can they be classified as legitimate military targets. If they support both military and civilian purposes, they can be regarded as “dual use objects.” Some commentators, such as Dinstein (p. 150), suggest that civilian infrastructure – e.g., bridges or railway lines – automatically become military objectives once hostilities commence, as they are potentially usable for troop movements or logistical purposes. Others caution that such a broad interpretation risks unduly eroding the protection afforded to civilian objects, as virtually any object could theoretically serve some indirect military purpose. For example, a more nuanced approach advocated by Schmitt (p. 385) requires a “reasonable likelihood” of military use that exceeds mere theoretical or remote possibilities. Still others emphasize that the criterion of “purpose” under Article 52(2) turns on actual intent to employ the object for military advantage (cf. AP I Commentary, para. 2022).

If reports are accurate and the Natanz, Esfahan, and Fordow facilities were indeed engaged in uranium enrichment of over 60%, they exceed the enrichment of 3-5% usually required for civil use fission (here). This suggests not only a ‘reasonable likelihood’ that the facilities were used for military purposes – it even points to the intent to do so. There is no plausible justification for enriching uranium to levels 15 to 20 times higher than those required for civilian energy production. Consequently, they would at least be regarded as dual-use objects and therefore lawful targets. The IDF reportedly considers these sites to be purely military objectives, implying that any harm to the facilities or their occupants is viewed as entirely military rather than collateral (Merriam/Schmitt, p. 25). From this perspective, collateral damage is, by definition, excluded for dual-use objects. Critics, however, caution that such an interpretation risks overlooking the civilian status of at least parts of the facilities and their personnel (Hathaway/Khan/Revkin p. 2735) – who remain protected under IHL unless and only for such time as they directly participate in hostilities.

Special Protection Awarded to Nuclear Sites?

Still, there is agreement (Dienstein, p. 150; Schmitt, p. 385 or Sassoli/Bouvier) that some objects are especially protected under IHL. Nuclear facilities differ significantly from classical military targets such as command centers, communications hubs, or conventional weapons manufacturing plants, because they are inherently hazardous and can pose significant risks to the surrounding civilian population if struck. Consequently, Article 56(1) AP I and customary law (ICRC, Rule 42) protect nuclear electrical generating stations and other “installations containing dangerous forces” such as dams and dykes, albeit with some caveats. Before we delve into these exceptions, it must first be scrutinized whether enrichment facilities are protected.

Whether uranium enrichment facilities that do not inhabit reactors fall within the ambit of Article 56(1) is highly contested. While some argue (Kolb, p. 149) that the list in Article 56(1) is illustrative rather than exhaustive, the negotiating history and the wording (see Zwanenburg) suggest otherwise. Attacks on other than the above named three targets are not subject to Article 56 AP I, even if they contain dangerous forces (here). States intentionally limited the scope of special protection to a narrowly defined set of installations presenting the gravest risks to civilian populations and refrained from extending this protection to the entire nuclear fuel cycle. Since Article 56(1) AP1 only protects stations that supply electricity (Kecskés, p. 511), not even INTC’s three research reactors fall within the scope of Article 56(1) AP1.

In any event, Article 56(1) AP I is not directly applicable to the present conflict, as neither Israel nor Iran are parties to AP I. Nevertheless, CIL requires heightened precautions in attacks on installations containing dangerous forces (ICRC, Rule 42). The object and purpose of this rule is to protect civilians from the release of hazardous forces-in this case, radioactive or chemical contamination-and to prevent severe civilian casualties. The customary norm’s protective rationale, according to the ICRC (ibid), should extend protective obligations towards other dangerous installations beyond the scope of Article 56(1) AP I. Thus, it is crucial whether the facility poses a genuine risk of releasing dangerous forces that would threaten civilian life in the region.

This is supported by State practice indicating that attacks against installations that contain dangerous forces should only be undertaken if the anticipated military advantage cannot be achieved by other means and if all feasible precautions are implemented to minimize risks to the civilian population. In this respect, it appears that Israel took at least some form of precautions for at least some of its strikes through warnings (see, e.g., here). On the afternoon of June 13, the IAEA stated that radiation levels could be managed with routine protective measures and that no radiation leakage had been detected outside the main uranium enrichment facility. At present, no dangerous release of radiation has been reported. This means that these facilities do not pose radiological hazards, but they do contain toxic chemical substances – such as uranium hexafluoride (UF6) – which can react with moisture to form dangerous compounds, potentially affecting nearby areas or even crossing borders depending on wind direction and speed. Pursuant to customary international law (ICRC, Rule 42), any attack on these types of facilities thus requires an elevated standard of precaution due to the risks posed to the civilian population.

The recent strikes on Iran’s nuclear infrastructure and the reported targeting of scientists raise complex legal questions under IHL. While certain components of the nuclear production cycle may qualify as military objectives – particularly where strong evidence suggests a direct contribution to weapons development – international humanitarian law imposes strict limits on how such operations are conducted. Civilian personnel remain protected unless directly participating in hostilities, and facilities containing hazardous substances are subject to heightened precautionary requirements under customary law. Ultimately, legality under IHL hinges not only on target classification but also on proportionality, precaution, and the protection of civilian life.