Israel's Use of Force: Legal or Dangerous Shift?

Is Israel Redrawing the Boundaries of International Law by Force?

How Israel’s Interpretation of Self-Defence Threatens the International Legal Order

Lovely Bernardo

For decades, Israel has invariably asserted the legality of its actions, presenting itself to the world as operating within the bounds of international law. This stance is evident in its historical rhetoric, beginning with the 1967 Six-Day War against Egypt, Jordan, and Syria, when it launched a "pre-emptive self-defence" against these Arab nations. Similarly, in 1981, Israel conducted the Osirak Reactor strike bombing Iraq, perceiving Iraq's nuclear weapons program as a potential threat that needs to be prevented (Little, 2017)." In 2007, during Operation Orchard in Syria, Israel carried out an airstrike based on suspicions of a nuclear reactor, adhering to its policy of preventive strikes against adjudged existential threats (Mumino, 2023). Most recently, Israel attacked Iranian nuclear and military targets under Operation Rising Lion, once again invoking “pre-emptive self-defence” against Iran’s alleged preparations for an imminent strike. While these actions may seem justified from national security standpoint, they raise a pressing question: can Israel’s evolving interpretation of self-defence, particularly the concept of pre-emptive force, be harmonised with the established framework of international law?

What exactly is pre-emptive self-defence, and does it hold up under international law?

The Legal Framework of Self-defence

The United Nations (UN) Charter provides under its Article 2 (4) the prohibition of the use of force against the territorial integrity or political independence of any state. The two primary exceptions to this prohibition are:

The purpose and intent of the law under this provision is to forbid both the use and the threat of force. While reprisals and retaliation were not explicitly mentioned in the Charter, the nature of Article 2(4) has been interpreted to ban such actions as illegal, and viewed them as counterproductive to the peaceful resolutions embedded within the UN framework (Bowett, 1972). Therefore, when a state attacks another state outside any of the exceptions outlined in the Charter, it violates the territorial integrity or political independence of the state being attacked. Such actions run afoul international law, and undermine peace and security.

The first exception is straightforward: authorisation from the UN Security Council would legitimise the use of force. However, this article does not intend to discuss that scenario. Instead, it will focus on the more contentious exception, which is, Article 51 of the UN Charter.

Article 51 of the United Nations Charter recognises the inherent right of states to self-defence “if an armed attack occurs.” Under this provision, a state is granted the ability to respond to aggression. However, this right is not unlimited and is not without exceptions. Actions taken in self-defence must adhere to the principles of necessity and proportionality; that is, defensive measures must be appropriate and limited to what is required to repel the attack and prevent further aggression (Gardam, 1993). Importantly, the International Court of Justice (ICJ) has repeatedly affirmed that the right to self-defence can only be invoked after an actual armed attack has occurred. The threshold for invoking Article 51 is intentionally high, excluding the use of force in anticipation of potential or speculative threats from its purview.

What Israel has to prove is that there exist an armed attack against their state, and their attack on Iran is self-defence, and therefore would not constitute a use of force affecting the territorial integrity or political independence of Iran.

What Is Publicly Known About the Israel-Iran Standoff?

Israel has been consistent in its claim that Iran poses an existential threat against them, focusing primarily on Iran’s nuclear program, not to mention its support for militant proxy groups, and their hostile ideas about the Iranian leaders.

The recent strike by Israel, was launched due to its assertion that Iran was preparing for an “imminent attack, against them (Israel Ministry of Foreign Affairs, 2025). They cited Iran’s continued uranium enrichment linked to nuclear weapon (Schaer, 2025). They maintained the legality of their strike and argued that it was an act of “pre-emptive self-defence” intended to neutralise imminent danger. The claim was based on an intelligence report (Fabian, 2025), but no publicly disclosed conclusive evidence indicated that Iran had finalised plans for an attack at the time of the airstrike.

On Iran’s side, it maintained that its nuclear activities were for peaceful purposes, following the Non-Proliferation Treaty. However, Iran has reportedly been amassing uranium beyond the 60%, which is technically below weapons grade, but above the civilian energy needs (Presse, 2025), which fueled suspicions. Also, its continued support for regional proxy groups, further bolsters tensions. However, none of the activities individually amounted to a direct armed attack on Israel, but they undisputedly contributed to the rising conflict between the two states (Al Jazeera, 2025).

Israel’s Legal Claim: Pre-Emptive or Anticipatory Self-defence

Israel argues that in certain extreme cases, the right of self-defence, as enunciated under Article 51 of the UN Charter, extends to pre-emptive or anticipatory self-defence. This means the use of force before an actual armed attack has taken place, but in anticipation of one that is imminent and unavoidable.

Pre-emptive self-defence is a controversial concept within international law that aims to adapt traditional self-defence to modern threats that may not constitute conventional armed attacks. The use of military force is generally prohibited under international law, except in certain circumstances. One lawful justification for using force is self-defence, which traditionally requires an actual armed attack or an immediate threat that is considered equivalent to an armed attack (Bothe, 2003). The concept of pre-emptive self-defence suggests that a threat can be so immediate and overwhelming that a state should not be required to wait until an attack has started to take defensive action. This principle relies on the necessity and immediacy components that are part of the customary international law.

The idea is rooted in the Caroline incident of 1837, a conflict between the U.S. and the British Empire (now Canada). It famously outlined the strict criteria for anticipatory (or pre-emptive) self-defence: the threat must be “instant, overwhelming, leaving no choice of means, and no moment for deliberation,” and the response must be proportionate to the threat (Jennings, 1938). This became known as the Caroline Doctrine, a foundational principle in customary international law (Norman and Trachtman 2005).

Critically, anticipatory (or pre-emptive) self-defence is distinct from preventive self-defence. The former concerns imminent threats; the latter involves speculative future dangers, which are not immediate or certain (Kasher, 2005). International law overwhelmingly rejects the latter as being unlawful.

Evaluating Israel’s Justification

Assuming, for the sake of argument, that pre-emptive self-defence is valid, the key question becomes: Does Israel's justification satisfy its strict requirements?

Israel’s assertion that its strike on Iran on June 13, 2025, was necessary to prevent an imminent attack. It cited Iran’s nuclear program, missile development, and proxy activities through Hezbollah as constituting an existential and immediate danger that justified a pre-emptive strike.

However, this concept is contentious when extended beyond immediate threats, such as when applied to perceived dangers where the threat is not yet fully evident.

Lack of Evidence of Imminence

For Israel’s anticipatory self-defence argument to be valid, there must be a real, immediate, and overwhelming threat, following the Caroline Test. However, there is no conclusive evidence that Iran currently possesses nuclear weapons. U.S. Director of National Intelligence Gabbard publicly stated that Iran has not resumed nuclear weapons development, and that Supreme Leader Khamenei had not reversed the 2003 suspension of the program. And that Iran does not appear to have nuclear weapon yet (Pereira, 2025).

In addition, Iran’s proxy activities, while seemed to be destabilizing, do not amount to an armed attack directly attributable to the Iranian state. To reiterate, under international law, the threshold for an armed attack that would justify self-defence is high. The ICJ in Nicaragua v. U.S. (1986) emphasised that only “the most grave forms of the use of force” qualify. Similarly, in the Oil Platforms case (2003), the ICJ ruled that even repeated attacks on shipping did not justify a use of force in self-defence.

In summary, Israel's military action is predicated not on verifiable imminent harm but rather on strategic assumptions. Although Iran's nuclear program and its support for proxy groups remain significant concerns, they may not constitute an immediate threat of nuclear proliferation or direct military confrontation with Israel. Such mere conjectures amount to suspicion, lacking concrete evidence of an immediate and overwhelming threat that would necessitate the use of force without deliberation. The legal threshold remains unmet, and there is no tangible harm that would justify invoking the Caroline doctrine for pre-emptive or anticipatory self-defence. What Israel has is merely an assumption of danger, not a clear and certain threat that would legally allow an armed attack and would cost civilian lives.

Israel’s Attack Fails the Tests of Necessity and Proportionality

Assuming arguendo that Israel’s claim is lawful under pre-emptive self-defence, the use of force must nonetheless comply with two fundamental requirements: (1) necessity and (2) proportionality. These are not optional criteria but core principles under both customary international law and Article 51 of the UN Charter, which remain binding even when a state responds to an imminent threat.

Was Force the Last Resort (Necessity)?

The principle of necessity refers to the requirement that a certain action must be indispensable to achieve a specific, legitimate aim. It requires that military force be used only as a last resort, after all peaceful means have been exhausted (Akande, 2013). Even in cases of imminent threat, as Israel argues, it must show that no other measures, diplomatic, economic, or legal, could have averted the danger. In the case of the strike on Iranian facilities, there is no public record showing that Israel attempted to engage international bodies, such as the UN, sought mediation through third-party states, or issued a formal ultimatum to Iran.

Moreover, U.S. and International Atomic Energy Agency (IAEA) assessments (as discussed) at the time indicated that Iran had not resumed nuclear weapons production, but only for the fact that there exist a higher amount of uranium collected, and that there was no clear evidence of a planned, immediate armed attack on Israel. These reports weaken the claim that the use of force was strictly necessary in these cases. If the threat was not truly imminent, then the justification for immediate and unilateral military action collapses.

Was the Force Used Excessive (Proportionality)?

Even if one accepts the argument that a strike was necessary, it must still be proportionate to the threat it poses. Proportionality requires that the use of force used must match the seriousness of the threat: the scale, duration, and intensity of the military action must commensurate with the aim pursued (Chainoglou, 2016). Under this standard, Israel’s armed attacks targeting multiple Iranian nuclear and military facilities, which have reportedly caused damage beyond the intended military objectives, raise concerns. Moreover, targeting and killing scientists are prohibited under international humanitarian law. Scientists are regarded as civilians unless they are directly involved in hostilities, which cannot currently confirm and would require separate legal analysis.

If the threat was speculative or undeveloped, then the response, particularly a broad and sustained bombing campaign, could be seen as punitive rather than defensive. Additionally, any harm to civilians, civilian infrastructure, or regional stability must be weighed in the proportionality analysis. The strike triggered retaliatory threats, disrupted diplomatic talks, and provoked a wider regional escalation, suggesting that the attack may have been disproportionate to any real or imminent danger.

U.S. Strike on Iran, Masquerading as Collective Self-defence

Following the Israel’s military operation, U.S. came into the picture and conducted its own airstrikes on Iranian nuclear facilities on June 22, 2025. These strikes, reportedly justified as acts of, again, self-defence and collective self-defence (Gill, 2025), or maybe a support for a strategic ally, representing a serious violation of international law. Not only did the U.S. act without a UN Security Council mandate, but it also invoked a distorted interpretation of collective self-defence that fails to meet the legal threshold under Article 51 of the UN Charter.

No Armed Attack, No Right to Collective Self-defence

Under Article 51 of the UN Charter, it also permits states to use force in collective self-defence only if an armed attack occurs against a member state. At the time of the U.S. strikes, Iran had not launched an armed attack against them. Without an actual attack, the legal trigger for self-defence was not met.

The U.S. strike on Iran was executed absent a Security Council resolution and without a clear, ongoing armed threat, violating  Article 2(4) of the UN Charter, which prohibits the use of force against the territorial integrity or political independence of another state. Such actions, undertaken in support of a preventive war, are categorically unlawful.

The U.S. may argue following the claim of Israel for an “imminent attack” would be outrageously flawed. International law does not permit one state to “borrow” the illegality of another’s use of force. Instead, the International Law Commission's Articles on State Responsibility opined that states are prohibited from participating in or aiding internationally wrongful acts, including illegal uses of force (International Law Commission, 2001). By launching its own strikes, the U.S. did not merely assist; it directly committed a separate breach of international obligations.

Dangerous Precedent for the Future

If Israel's long-standing interpretation of pre-emptive self-defence were accepted, it would essentially transform Article 51 into a carte blanche for powerful states to launch pre-emptive strikes based not on actual attacks but on secret intelligence, perceived threats, and political assumptions. Worse, allowing the U.S. to frame its strike as lawful collective self-defence is dangerous. Permitting powerful states to launch attacks under vague or speculative threats, will legitimise a world where military might is right, and alliances become licenses for war. We have seen how Israel called for U.S. support publicly, we heard it, and the world was watching.

This would significantly undermine the prohibition on the use of force, destabilise the already fragile global legal order, and contravene international and customary law. As Professor Ben Saul warns:

“International law is only law if we demand that our allies, not only our adversaries, obey it. If we apply it selectively, we cannot expect others to respect it, or respect us” (Saul, 2025).

In reality, what Israel refers to as "pre-emptive self-defence" is actually preventive war, something that international law does not recognise as legitimate. Professor Marko Milanovic affirms:

“Even the broadest understanding of anticipatory self-defence was taken as correct, Israeli’s use of force against Iran would be illegal” (Milanovic, 2025).

But this is not just a legal debate, this has human consequences. Allowing such actions to go unchallenged risks tearing at the fabric of the fundamental rules that restrain aggression between states. When one state redraws the rules of engagement, others will follow. And the world will inch closer to a future where missiles come before dialogue, and destruction precedes diplomacy.

If international law is to retain its significance, states must not be allowed to expand the concept of self-defence into a justification for unilateral military action. While nuclear threats must indeed be treated with utmost seriousness and importance, international laws exist to be adhered to, not manipulated. Israel may be redrawing the boundaries of international law, but the world must decide whether it will stand by, as those lines are erased.

References

Agence France-Presse. (2025, June 29). Iran will likely be able to produce enriched uranium in a matter of months, IAEA chief says. The Guardian. https://www.theguardian.com/world/2025/jun/29/iran-will-likely-be-able-to-produce-enriched-uranium-in-a-matter-of-months-iaea-chief-says

Akande, D. (2013). Necessity and proportionality in jus ad bellum and jus in bello. In M. Weller (Ed.), The Oxford handbook of the use of force in international law (pp. 307–333). Oxford University Press.

Al Jazeera. (2025, June 14). Iran denies nuclear weapons intentions amid Israeli accusations. Al Jazeera. https://www.aljazeera.com

Bothe, M. (2003). Terrorism and the legality of pre-emptive force. European Journal of International Law, 14(2), 227–240. https://doi.org/10.1093/ejil/14.2.227

Bowett, D. W. (1972). Self-defence in international law. Manchester University Press.

Chainoglou, K. (2016). Proportionality in the law of armed conflict. In B. Saul & D. Akande (Eds.), The Oxford guide to international humanitarian law. Oxford University Press.

Fabian, E. (2025, June 13). Israel launches strikes on Iranian targets over nuclear threat. The

Times of Israel. https://www.timesofisrael.com

Gardam, J. (1993). Necessity, proportionality and the use of force by states. Cambridge University Press.

Gill, T. D. (2025). Collective self-defence or collective aggression? Legal challenges after the US-Iran airstrikes. Journal of Conflict & Law, 42(1), 55–68.

Gray, C. (2018). International law and the use of force (4th ed.). Oxford University Press.

International Court of Justice. (1986). Military and Paramilitary Activities in and Against

Nicaragua (Nicaragua v. United States of America), Merits. I.C.J. Reports 1986, p. 14.

International Court of Justice. (2003). Oil Platforms (Iran v. United States of America), Judgment. I.C.J. Reports 2003, p. 161.

International Law Commission. (2001). Draft articles on responsibility of states for internationally wrongful acts, with commentaries. Yearbook of the International Law Commission, 2001, Vol. II, Part Two. https://legal.un.org/ilc/texts/instruments/english/commentaries/9_6_2001.pdf

Jennings, R. Y. (1938). The Caroline and McLeod Cases. American Journal of International Law, 32(1), 82–99. https://doi.org/10.2307/2190632

Kasher, A. (2005). The ethics of anticipatory war. In Y. Dahan (Ed.), The Philosophy of War (pp. 133–153). Tel Aviv University Press.

Little, D. (2017). The Osirak option: Israel's attack on Iraq's nuclear reactor and U.S. nonproliferation policy. Middle East Journal, 71(1), 9–33.

Milanovic, M. (2024, April 19). Is Israel’s use of force against Iran justified by self-defence? EJIL: Talk! https://www.ejiltalk.org/is-israels-use-of-force-against-iran-justified-by-self-defence/

Norman, G., & Trachtman, J. P. (2005). The Customary International Law Game. American Journal of International Law, 99(3), 541–580. https://doi.org/10.2307/1602291

Pereira, S. (2025, June 14). US intelligence says Iran nuclear program not yet weaponized. The Washington Post. https://www.washingtonpost.com

Schaer, C. (2025, June 12). Iran enriches uranium beyond 60%, IAEA raises concern. Associated Press. https://apnews.com

Saul, B. (2025, June 16). Australia’s claim that Israel has a right to defend itself against Iran is inconsistent with our rules-based order. The Guardian. https://www.theguardian.com/commentisfree/2025/jun/16/australias-claim-that-israel-has-a-right-to-defend-itself-against-iran-is-inconsistent-with-our-rules-based-order

The Guardian,