A nuclear terrorist does not match the profile of a suicide bomber or spree gunman. It’s not someone building a nuclear weapon in a cave from a box of scraps. A nuclear terrorist, rather, could be hiding in plain sight in a mid-tier government post.
Such a person could be active in Iran, right now, motivated to build an improvised nuclear weapon after an opportunity to steal weapon-usable uranium—enriched at 60 percent uranium 235—has just presented itself. This person could be emboldened by the absence of IAEA inspectors overseeing Iran’s known stockpile of fissile material.
Despite popular confusion about the nature of critical masses and what level of enrichment can be used for a weapon, a technical companion shows that as little as 40 kilograms of 60-percent-enriched uranium, representing only 10 percent of Iran’s stockpile, could be used to build a crude gun-type weapon like the “Little Boy” bomb that destroyed Hiroshima with an explosive yield of several kilotons. Such a weapon requires no further enrichment, greatly simplifying and fast-tracking construction.
The question, therefore, is not whether Iran can achieve its nuclear ambitions, but whether and how these can be realized by nuclear terrorists without state approval.
If not by air, then by cargo. In their letter to US President Franklin D. Roosevelt, Leo Szilard and Albert Einstein suggested that a nuclear weapon may be too heavy to be delivered by air, but could be brought into a port in a cargo container and detonated. Such a scenario is feasible for aspiring nuclear terrorists in Iran. While the technical hurdles of building a nuclear weapon have long been discussed, they may not be insurmountable to a well-resourced group of clandestine sub-state actors.
As of July 2025, publicly available intelligence was inconclusive about what remains of Iran’s enrichment capabilities and other nuclear assets following the June attacks by Israel and the United States on its nuclear facilities. Some experts have suggested, reasonably so from a tactical perspective, that Iran may have removed part of its enriched uranium stockpile from the Fordow underground enrichment facility and scattered it into multiple secret caches, perhaps even in otherwise innocuous non-military storage facilities, to prevent the United States and Israel from destroying the entire stockpile and equipment in a single decapitating strike. Although hypothetical, such caches could create as many opportunities to intercept material in transport as it would to recruit a co-conspirator to help steal some.
Where from inside the Iranian leadership? To understand how a mid-level official might take such actions, it is essential to examine the structure of power and ideology within the Islamic Republic.
The Islamic Republic of Iran is governed through a hybrid political-theocratic structure, ultimately ruled by Supreme Leader Ayatollah Ali Khamenei. While formal executive, legislative, and judicial institutions exist, real power lies in unelected bodies and individuals loyal to the Supreme Leader. Among them, the Guardian Council vets all candidates for conformity to Islamic ideology, and the Assembly of Experts, a body of clerics, is officially supervisory to the Supreme Leader, but practically subservient to him.
The Supreme Leader also controls all major military and intelligence appointments, including the direct command of the IRGC, a parallel military and political institution separate from the traditional armed forces. Unlike the Iranian army, which is tasked with conventional defense and is generally apolitical, the IRGC is an ideological military organization that was formed after the 1979 revolution to protect the regime. Over the years, the IRGC has evolved into a sprawling enterprise with external and domestic military and intelligence branches, and also controls a vast array of holdings in all key sectors of the Iranian economy.
The mullahs, particularly the aging clerical elite, are at an all-time low in favorability among Iranians, and might also be seen by some within the regime as cynical power-retainers and no longer as revolutionaries, contrary to the regime’s policy of sustaining and exporting the ideology of the revolution. Their support for nuclear weapons is often symbolic—meant to deter foreign intervention and preserve the regime, rather than to ever actually use them. Many mullahs, therefore, see nuclear weapons as a tool for political leverage. Khamenei himself has repeatedly spoken against the use of nuclear weapons, but never officially opposed their development for deterrence.
Whether or not Khamenei actually issued a fatwa (strict religious decree) in 2003 that forbids the acquisition of nuclear weapons, a motivated cabal may not be deterred because they could consider this decree not a real ruling to be enforced, but one meant to be disregarded as propaganda for foreigners. Regardless, there are hundreds of mullahs within the Iranian government, and only one would be enough to divert the resources necessary to build a crude nuclear weapon.
By contrast, many within the IRGC—particularly younger or mid-career officers—are genuine religious, ideological adherents who see themselves as true heirs to the 1979 revolution and therefore of Khamenei’s rule. Some even harbor messianic and apocalyptic beliefs, especially those within or influenced by the more hardline factions of the Quds Force or Basij—two paramilitary branches of the IRGC.
What for? The catastrophic loss of senior officials and infrastructure during the so-called “12-day war” between Israel, supported by the United States, and Iran in June was, for many regime insiders, not merely a military defeat but a profound humiliation. For some, this may have resulted in a loss of faith in the regime’s ideology, while for others, it could catalyze the initiative to take redemptive action and press ahead with building one or several nuclear weapons. A disillusioned, yet ideologically committed, IRGC officer might view unilateral action such as a nuclear attack against Israel as necessary to rekindle the revolutionary spirit of the late 1970s and reestablish the deterrence that preceded the October 7, 2023 attacks. With the regime losing face and at its weakest point in its 46-year history and recent progress in Iran’s nuclear technology and fissile material production, the risk is the highest now that one or a group of IRGC or Quds Force officers takes matters into their own hands. The conspirators need not be suicidal either. The international response to any nuclear terrorist attack would be certain to be devastating to the Iranian regime, even if it did not give explicit approval for such an operation. This could be an opportunity for conspirators to place the blame on the regime leadership, mount a coup, and take power in Iran.
A comprehensive coup need not be the motivation of a cabal, though. If the incentive is the return of glory to the regime establishment, the aspiring terrorists could offload liability to ideological partners within the regime’s proxies, such as Hezbollah, Hamas, or the Houthis. Like the regime in Iran, the leaders of these organizations are generally self-preserving; those who are not tend to be quickly replaced by those who are. As such, proxies may be hesitant to participate in such a scheme for fear that its success could destabilize their patron regime in Iran. However, there are certainly abundant middle-tier members who may have received their posts for ideological reasons and who may be more easily recruited by the cabal. The cabal may not necessarily have to take responsibility for all the technical challenges, such as uranium conversion, material acquisition and machining, and weapon delivery. Small numbers of technicians with access to relatively common industrial equipment could handle most of the work, and could be bribed, deceived, or placed under duress to do so if they are not ideologically driven to participate.
These conspirators and their motivations are completely imagined. But the opportunity for a nuclear terrorist to siphon uranium from Iranian stockpiles is very real, and may be the greatest risk of nuclear terrorism ever encountered. This risk could be reduced significantly with robust IAEA access to the known Iranian stockpile: The earlier any missing uranium is detected, the less any sort of nuclear terrorist scheme would likely succeed.