The International Atomic Energy Agency (IAEA) has long served as the world’s nuclear watchdog, tasked with verifying that civilian nuclear programs remain peaceful under the Nuclear Non-Proliferation Treaty (NPT). For Iran, however, that verification has become severely strained. As of mid-2025, the IAEA possessed detailed estimates of Iran’s enriched uranium inventories. Since Israeli and U.S. strikes on key nuclear sites in June 2025, those assessments have frozen. The agency now lacks access to facilities, rendering it unable to confirm the current size, location, or condition of Iran’s stockpile—particularly its most sensitive holdings of highly enriched uranium (HEU).

This breakdown in monitoring represents one of the most significant proliferation concerns in recent years. Iran’s accumulation of uranium enriched to 60 percent U-235—close to the roughly 90 percent considered weapons-grade—had already drawn sharp international scrutiny before the conflict. The material’s existence, combined with Iran’s advanced centrifuge infrastructure, shortened the theoretical “breakout” time needed to produce enough fissile material for nuclear weapons. Today, the IAEA cannot verify whether that stockpile remains intact, has been moved, or suffered damage.

Background on Iran’s Enrichment Program

Iran’s nuclear program dates back decades, but its enrichment activities accelerated after the 2018 U.S. withdrawal from the 2015 Joint Comprehensive Plan of Action (JCPOA). Under the original deal, Iran was limited to enriching uranium to no more than 3.67 percent U-235 and stockpiling no more than 202 kilograms of that low-enriched uranium (LEU). Enrichment centrifuges were also capped.

Following the U.S. exit and the reimposition of sanctions, Iran progressively exceeded those limits. It began producing uranium enriched to 20 percent and then, starting in 2021, to 60 percent—the highest level ever achieved by a non-nuclear-weapon state under IAEA safeguards. This escalation occurred at declared facilities: the Natanz Fuel Enrichment Plant, the Fordow Fuel Enrichment Plant (built deep inside a mountain), and associated sites at Isfahan (Esfahan).

Uranium enrichment increases the concentration of the fissile isotope uranium-235. Natural uranium contains only about 0.7 percent U-235. For nuclear power reactors, 3–5 percent enrichment suffices. Research reactors may use 20 percent. Weapons-grade material requires around 90 percent. The jump from 60 percent to 90 percent demands far less separative work (measured in SWU) than earlier stages. Analysts note that Iran’s pre-strike 60 percent stock could, in theory, be further enriched relatively quickly into weapons-usable material.

IAEA’s Pre-Strike Estimates

According to IAEA reports and analyses of data up to June 13, 2025—the day major strikes began—Iran’s enriched uranium stockpile in the form of uranium hexafluoride (UF6) totaled approximately 9,040.5 kilograms (uranium mass). This broke down as:

• 440.9 kg enriched up to 60 percent U-235
• 184.1 kg enriched up to 20 percent U-235
• 6,024.4 kg enriched up to 5 percent U-235
• 2,391.1 kg enriched up to 2 percent U-235

An additional roughly 834 kg existed in other chemical forms, such as oxides, fuel assemblies, and scrap. The total enriched uranium inventory reached around 9,875 kg when including all forms.

The 60 percent stock had grown steadily. Between earlier reporting periods and mid-June 2025, it increased by tens of kilograms, consistent with Iran’s production rates at the time. This material was stored primarily at the three main sites: Natanz, Fordow, and especially the underground tunnel complex at Isfahan. The IAEA had been tracking production, movements, and inventories through on-site inspections, cameras, and seals until access was curtailed.

These figures mattered because of their proliferation potential. A “significant quantity” for safeguards purposes is the approximate amount of nuclear material for which the possibility of manufacturing a nuclear explosive device cannot be excluded—roughly 25 kg of 90 percent enriched uranium for one weapon (accounting for processing losses). Iran’s 60 percent holdings represented multiple significant quantities if further enriched.

The June 2025 Strikes and Immediate Aftermath

In June 2025, Israel and the United States conducted strikes on Iranian nuclear facilities, including Natanz, Fordow, and Isfahan. Damage assessments varied: above-ground structures at Natanz were heavily impacted, while underground areas sustained uncertain effects from power disruptions or blasts. Fordow, deeply buried, reportedly saw limited structural damage in some accounts. Isfahan’s tunnel complex—used for storing higher-enriched material—suffered entrance damage but appeared largely intact internally according to later satellite imagery.

Iran’s Foreign Minister later described the enriched uranium as being “under the rubble.” IAEA Director General Rafael Grossi assessed that much of the stockpile, including a substantial portion of the 60 percent material, likely remained inside the damaged sites, particularly the Isfahan tunnels. Satellite imagery analyzed by independent experts showed ongoing activity at some entrances—rubble clearance and hardening—but no clear evidence of large-scale removal of sensitive material.

Crucially, IAEA inspectors were withdrawn or denied access after the strikes. Iran suspended cooperation with the agency in key areas, passing legislation limiting inspections. This created an immediate and ongoing gap in knowledge.

Current Status: Loss of Continuity of Knowledge

In its June 2026 quarterly report to member states, the IAEA stated it could not provide information on the current size, composition, or whereabouts of Iran’s enriched uranium stockpile. It also could not verify whether enrichment activities, including research and development, had been suspended. Verification of the previously declared HEU inventory—already overdue by standard safeguards timelines—remains impossible without resumed access.

Grossi has publicly expressed that the agency believes the bulk of the near-weapons-grade material is still at Isfahan, with smaller amounts possibly at Fordow or Natanz. He has emphasized the difficulty of recovering or handling the material, noting it exists in cylinders of highly radioactive UF6 gas. Iranian officials have given mixed signals, sometimes claiming no plan to recover it and at other times engaging in broader diplomatic discussions.

Satellite imagery continues to show activity around affected sites, but this provides only indirect clues. No confirmed diversion or large-scale movement of the stockpile has been publicly verified. The IAEA has highlighted “serious concern” over both the quantity of HEU produced and stored and the prolonged lack of access.

Broader Implications

The situation carries significant non-proliferation risks. Even if damaged or buried, the 60 percent uranium represents a latent capability. Recovering and further enriching it would require time, specialized equipment, and safe handling—challenges amplified by physical destruction and potential radiation hazards. However, the material’s existence shortens any future breakout timeline if Iran regains operational capacity.

Internationally, the stockpile has featured in diplomatic efforts to de-escalate tensions. Discussions around interim arrangements or broader deals have referenced down-blending or accounting for the HEU. The IAEA has repeatedly called for Iran to facilitate verification, warning that the lack of continuity of knowledge undermines confidence in the peaceful nature of the program.

For the agency itself, the episode tests its safeguards system. Decades of monitoring at declared sites built a detailed baseline. That baseline is now unverifiable. Re-establishing it will require extensive Iranian cooperation, new inspections, and possibly advanced techniques to account for any discrepancies.

Outlook

As of July 2026, the IAEA’s knowledge of Iran’s HEU stockpile remains anchored to its last verified snapshot from June 2025: roughly 441 kg of 60 percent enriched uranium, plus substantial lower-enriched holdings, stored across Natanz, Fordow, and Isfahan. Everything since—the physical status of that material, any production or processing, and its precise locations—lies beyond confirmed reach.

Director General Grossi and member states continue to press for resumed access. Until inspectors return and Iran provides full cooperation, the world will rely on estimates, satellite imagery, and statements rather than direct verification. The 60 percent stockpile, once a symbol of Iran’s advancing technical capabilities, has become a symbol of the fragile state of nuclear transparency in the region.

Resolving this uncertainty is essential not only for non-proliferation but for any credible path toward renewed diplomatic engagement. The IAEA’s role remains central: only through independent, on-the-ground accounting can confidence be restored that Iran’s nuclear activities stay exclusively peaceful. Until then, the precise fate of one of the world’s most closely watched nuclear material stockpiles stays hidden beneath layers of rubble, politics, and restricted access.

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