The killing of Ayatollah Ali Khamenei in the opening phase of the US-Israeli war against Iran has generated a striking argument in strategic and theological circles alike: that the killing may have removed not merely a political leader but a normative brake on Iran’s possible march toward nuclear weapons. Reports indicate that Iranian decision-making has since hardened under intense military pressure and an increasingly securitised internal environment.

What gives Khamenei’s death a particular doctrinal significance is that he had, over more than two decades, publicly framed weapons of mass destruction—including nuclear and chemical weapons—as contrary to Islam. If that position represented a genuine religious constraint rather than mere diplomatic rhetoric, then his death may have removed more than a leader: it may have weakened the doctrinal restraint that helped keep Iran a threshold nuclear state.

What gives Khamenei’s death a particular doctrinal significance is that he had, over more than two decades, publicly framed weapons of mass destruction—including nuclear and chemical weapons—as contrary to Islam.

Islamic just war theory places moral constraints on indiscriminate violence, constraints that Khamenei appeared to project onto state policy. With that authority now gone, the central question is whether a moral tradition can discipline a state that increasingly experiences its insecurity as existential. Whether the next supreme leader can impose doctrinal restraint on a system drifting toward hard security logic.

The Islamic just war theory

The Islamic conception of war begins from a premise different from the caricatures often projected onto it. Classical Islamic thought does not treat war as an unbounded field of religious violence. Rather, it regulates warfare through a moral-legal framework derived from the Qur’an, the practice of the Prophet, and the juristic traditions that developed in subsequent centuries. The foundational Qur’anic injunction is taken from verse 2:190: “Fight in the way of God those who fight you, but do not transgress. Indeed, God does not love transgressors.” The verse both permits fighting and limits it: war is accepted as a political reality, but not treated as morally autonomous.

The Islamic conception of war begins from a premise different from the caricatures often projected onto it. Classical Islamic thought does not treat war as an unbounded field of religious violence.

The duality of permission and restraint thus runs through the Islamic just war tradition. War may be legitimate in cases of defence, resistance to aggression, or protection of the community. But even a just cause does not license unlimited means. Islamic jurists emphasised proportionality, legitimate authority, fidelity to agreements, and the protection of non-combatants—including women, children, the elderly, monks, and peasants— developing a norm of discrimination that restricted violence to active combatants.

It is from this perspective that nuclear weapons become especially difficult to reconcile with Islamic ethics. A weapon whose essence is mass, uncontrolled devastation, sits uneasily with any tradition that treats non-combatant immunity as morally central. In Islamic terms, the problem is not simply the scale of destruction, but the very structure of the act: the means themselves are transgressive.

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 The fatwa: Genuine constraint or strategic cover?

Ayatollah Ruhollah Khomeini’s reputed opposition to chemical weapons during the Iran-Iraq War established an early precedent for this kind of doctrinal restraint. Iraq used chemical agents extensively, and Iran suffered enormously—some 20,000 Iranians were killed and over 100,000 severely injured. Yet the Islamic Republic did not respond in kind on a comparable scale. Whether that restraint was entirely theological or also strategic remains debated. Recent evidence suggests limited Iranian chemical weapons development during the war. Still, the episode reinforced the notion that certain weapons lay beyond the moral threshold that Iran’s clerical leadership was prepared to cross openly.

Khamenei extended this logic to the nuclear realm. He first issued an oral fatwa in October 2003 declaring nuclear weapons as forbidden (haram) in Islam, and repeated this position in an official statement at the emergency meeting of the International Atomic Energy Agency in August 2005. Over subsequent years, Iranian officials repeatedly invoked his religious decree as evidence of the Islamic Republic’s peaceful nuclear intentions.

Khamenei extended this logic to the nuclear realm. He first issued an oral fatwa in October 2003 declaring nuclear weapons as forbidden (haram) in Islam, and repeated this position in an official statement at the emergency meeting of the International Atomic Energy Agency in August 2005.

But the fatwa’s authenticity and legal weight have always been contested. Some have argued that no formal written fatwa was ever issued and that what Iran marketed as a religious ruling was, in origin, merely the closing paragraph of a message to a 2010 nuclear disarmament conference, later retroactively framed by Iranian diplomats as a fatwa. Others have documented that Khamenei’s pronouncements on nuclear weapons were inconsistent: at times he categorically forbade development, stockpiling, and use; at other times he appeared to permit development and stockpiling while forbidding use.

None of this entirely strips the fatwa of significance. In political systems where legitimacy is partly theological, a public prohibition articulated by the supreme jurist, even if ambiguous in its legal form, raises the political and doctrinal cost of reversal. As one scholar observes, such declarations make it costly for the Islamic Republic to overturn the publicly stated position even if they do not constitute binding juridical rulings in the formal sense.

Succession and the question of doctrinal inheritance

The critical question of whether Khamenei’s successor would inherit his political and moral authority looms large. On March 9, 2026, the Assembly of Experts named Mojtaba Khamenei, the 56-year-old son of Ali Khamenei as Iran’s third supreme leader. Whether he would inherit his father’s doctrinal commitments, especially on nuclear weapons, is far from clear. Not known as a jurist of comparable standing to his father, Mojtaba’s authority derives primarily from his revolutionary and security credentials rather than from the depth of his theological learning, a fact noted critically within Iran’s clerical establishment, which has historically resisted father-to-son succession as uncomfortably monarchical.

Khamenei’s nuclear prohibition carried weight because it came from the state’s highest religious authority. Mojtaba’s standing is far more contested, which means that any comparable prohibition would likely carry less doctrinal force—while any tacit relaxation would accelerate the erosion of the barrier his father maintained. The IRGC commanders who manoeuvred his appointment to power have long been among those pressing for a reassessment of Iran’s nuclear posture.

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Islamic restraint vs strategic realism

This leads to the final and perhaps hardest question: would Iran, if acting as a pure realist state, pursue nuclear weapons regardless of the Islamic just war tradition? The realist answer is straightforward. States seek survival in an anarchic international system. When a state faces stronger adversaries, recurring coercion, and the credible prospect of regime-change violence, it has every incentive to pursue the ultimate deterrent. From this perspective, the logic of nuclear acquisition is not theological but strategic: a bomb would promise not battlefield utility but regime survival, deterrence, and insulation from future attack.

Khamenei’s nuclear prohibition carried weight because it came from the state’s highest religious authority. Mojtaba’s standing is far more contested, which means that any comparable prohibition would likely carry less doctrinal force—while any tacit relaxation would accelerate the erosion of the barrier his father maintained.

And yet Iran is not a pure realist state in the abstract. It is a political order where ideology, clerical authority, national security, and regime survival have long coexisted in uneasy combination. The more interesting possibility, therefore, is not that realism simply replaces theology, but that realism gradually colonises it. In that scenario, doctrine is not openly discarded; it is reinterpreted and subordinated to necessity, allowing the state to retain Islamic language while moving toward a posture that the older Khamenei publicly resisted.

The greater danger is that the Islamic Republic’s language of restraint may cease to anchor policy and instead begin to trail behind it. If so, Iran’s nuclear future will be decided not only in centrifuge halls or command bunkers, but in the struggle between theological limits and strategic fear.

The views expressed in this article belong to the author and do not necessarily reflect the editorial policy of Middle East Monitor.

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