The assassination of Iranian supreme leader Ali Khamenei by the US and Israel this month has left the Middle East and the world confronting an important question: Is his famous fatwa prohibiting the production and usage of nuclear weapons also dead?
Before answering this question, we need to look at the history of that fatwa and fact-check it to understand, from both a religious and political point of view, whether this policy survives when its architect is dead, and whether the new supreme leader, Ali Khamenei’s son Mojtaba, is therefore bound by it.
For decades, the late supreme leader consistently asserted that nuclear weapons were prohibited under Islamic law. Iranian officials frequently referred to this stance, indicating that Tehran’s nuclear programme was determined by both strategic and religious considerations.
However, there was never a clear text of the fatwa publicly available. Instead, the elder Mr Khamenei’s website summarised it by saying he “strongly and repeatedly announced that building and using nuclear weapons is a sin [haram] and therefore is banned from a religious and Islamic point of view.
In 2021, during a meeting with members of the Assembly of Experts, one of Iran’s most powerful governing bodies, he argued that Tehran cannot be prevented from building or obtaining nuclear weapons, but has nonetheless chosen not to do so.
“Some people [..] constantly say that they will not let us build a nuclear weapon. But who are you to prevent Iran from building a nuclear weapon? If we decided to build a nuclear weapon, you and powers greater than you would not be able to stop us. But we have not decided to do so based on our Islamic thinking,” he explained.
With his assassination by the US and Israel, and the power transferring to Mojtaba Khamenei, the influence of this restraint may diminish. While religious rulings last beyond the issuing cleric's life, their authority depends on reaffirmation by successors.
Should the new supreme leader decline to restate the prohibition, or simply ignore it and stop mentioning it, the supposed religious barrier that has shaped the country’s nuclear narrative could erode, potentially enabling a shift in Iran’s nuclear doctrine at a time of war. Many western countries have long accused Iran of pursuing nuclear weapons despite the "nuclear fatwa" but removing that constraint in Iran would change the calculus completely and could expose the region to the risk of much larger confrontations.
This issue is significant because Iran is widely regarded as a nuclear threshold state. Despite US strikes last June, which President Donald Trump claimed obliterated the nuclear programme, the country still possesses advanced uranium stockpiles enriched much closer to weapons-grade. The primary concern is not that Iran might possess a nuclear weapon now, but that it could develop one rapidly if a political decision were made. The country also has ballistic missiles capable of reaching Israel and much of the Middle East.
Inside Iran, the debate over nuclear weapons focuses on whether possessing such weapons would strengthen the regime or increase its vulnerability.
Advocates of restraint argue that developing those weapons would provoke severe retaliation. Others refer to countries such as North Korea to argue that nuclear capability can deter efforts at regime change. Ali Khamenei's death eliminates the religious authority that previously influenced this debate. His son could be less radical or even more so. It is yet to be seen.
Nevertheless, the threshold for nuclear use is extremely high. Israel, widely believed to possess nuclear weapons while it officially maintains ambiguity on the subject, is thought to regard them as a deterrent of last resort rather than as battlefield weapons. Israel's first use of a nuclear weapon would entail high costs, including isolation, the risk of unpredictable escalation and an end to the ambiguity policy.
The US doctrine, meanwhile, specifies that nuclear weapons should be employed only in extreme circumstances to defend vital interests. In practice, the US’s overwhelming conventional capabilities permit strategic strikes without resorting to nuclear weapons.
Another important factor is leadership personalities. Although less decisive in this regard, they inevitably influence calculations. Two figures stand out here: Mr Trump, who is unpredictable and deeply concerned with his image and post-presidential legacy; and Israeli Prime Minister Benjamin Netanyahu, who has launched wars on several fronts not only to reshape the Middle East in his country’s favour but also to go down in the history books as the man who eliminated the most significant threats to his country's security, rather than the leader who witnessed Israel's most significant intelligence failure on October 7, 2023.
Historically, miscalculation and leadership styles during crises, rather than deliberate first use, have represented the greatest nuclear risk. Vague warning signals, misinterpreted intelligence or rapidly escalating conventional conflicts frequently trigger nuclear alarms.
The use of nuclear weapons in the Middle East would have consequences extending well beyond the immediate battlefield. A single detonation over any city could result in extensive civilian casualties and widespread radioactive fallout. Politically, such an event would break the global nuclear taboo that has persisted since the end of the Second World War and profoundly change the regional and global security environment. States might determine that nuclear weapons are now a means of guaranteeing survival, triggering a new wave of proliferation.
For decades, Iran’s leadership portrayed religion as a barrier to obtaining and using nuclear weapons. The death of Mr Khamenei would not automatically eliminate his "fatwa", according to many scholars, but it would transfer final judgment over its continued relevance to his successor. Whether Mojtaba Khamenei chooses to reaffirm the nuclear prohibition or quietly allow Iran’s nuclear doctrine to evolve may now become one of the most consequential questions controlling the region’s unfolding war.
