UN nuclear inspectors at Iran’s Fordow facility encountered a significant intelligence gap last year when trucks arrived carrying advanced uranium-enriching centrifuges into the underground site near Tehran. Although Iran had informed the International Atomic Energy Agency (IAEA) about the planned installation of hundreds of IR-6 centrifuges, inspectors were left uncertain about the origin of these sophisticated machines, according to a source close to the UN monitoring efforts.

This incident highlights a broader problem: since former U.S. President Donald Trump withdrew from the 2015 nuclear agreement, which imposed strict limits and oversight on Iran’s nuclear program, the IAEA has lost track of some crucial aspects of Tehran’s activities.

IAEA reports reveal ongoing blind spots, including incomplete knowledge about the total number of centrifuges Iran currently owns, where these machines and their components are manufactured or stored, and the inability to conduct surprise inspections at undeclared sites. These gaps significantly hinder the agency’s ability to verify Iran’s nuclear ambitions.

As the U.S. and Iran resume negotiations aimed at reinstating nuclear constraints on Tehran, experts emphasize that addressing these monitoring weaknesses is essential. Officials, diplomats, and analysts familiar with the issue warn that without closing these gaps, any deal would lack credible verification.

Ali Vaez, director of the Iran Project at the International Crisis Group, stressed, “We need a clear baseline understanding of the scale and scope of Iran’s nuclear activities. Piecing this together could take months, but it’s vital for building trust in any agreement’s non-proliferation commitments.”

Iran, for its part, maintains that following the U.S. withdrawal from the 2015 deal, it no longer owes enhanced transparency to the IAEA and rejects accusations of pursuing nuclear weapons. It insists its nuclear program is peaceful, even as it has made substantial progress in uranium enrichment.

When the 2015 accord was implemented, it capped Iran’s uranium enrichment at below 4%, thereby lengthening the “breakout time” — the period required for Iran to accumulate weapons-grade material — to at least a year. Today, that timeframe has nearly vanished, as Iran enriches uranium up to 60% purity, approaching weapons-grade levels of approximately 90%.

A confidential IAEA report reveals Iran currently possesses enough highly enriched uranium that, if further refined, could fuel up to nine nuclear warheads. The watchdog notes that no other non-nuclear weapons state has enriched uranium to such levels. Typically, nuclear power plants use uranium enriched to just 3-5%.

A European official familiar with the situation told Reuters that Iran’s enrichment infrastructure is now so advanced that it could quickly rebuild its program even if it were shut down.

After five rounds of U.S.-Iran talks, major hurdles remain, including Iran’s refusal to abandon uranium enrichment altogether or to transfer its stockpile of highly enriched uranium abroad. With the window to restore the longer breakout time of the 2015 deal closed, any new pact will likely need to strengthen IAEA monitoring significantly.

Around three years ago, Iran ordered the removal of surveillance equipment installed under the 2015 agreement, including cameras that tracked centrifuge production facilities. By then, the IAEA had already lost access to this footage for over a year.

While inspectors can see roughly 20,000 centrifuges currently operating, the agency lacks reliable information on how many more have been produced recently and remain undisclosed.

A U.S. State Department spokesperson underscored the importance of IAEA monitoring to fully understand Iran’s nuclear program but noted that Washington prefers not to discuss sensitive negotiation details publicly.

Iran continues to abide by some obligations under the Non-Proliferation Treaty, which permits uranium enrichment but demands nuclear technology be used solely for peaceful purposes. However, the country’s enrichment levels and centrifuge advancements far exceed the limits set by the 2015 deal.

IAEA chief Rafael Grossi recently emphasized that Iran must accept “indispensable” restrictions and allow rigorous inspections to reassure the international community of its peaceful intentions. Yet, the agency currently states it cannot guarantee that Iran’s nuclear activities are exclusively peaceful.

Diplomats anticipate that any future agreement will require the IAEA to establish a comprehensive “baseline” — a detailed snapshot of all aspects of Iran’s nuclear program. Achieving this will be challenging, as many gaps have persisted for years and may never be fully resolved.

Eric Brewer, a former U.S. intelligence analyst now with the Nuclear Threat Initiative, noted, “Reconstructing this baseline will be difficult and depends heavily on Iran’s cooperation. Even then, uncertainty will remain.”

The critical question, he added, is whether the United States is willing to accept this degree of uncertainty in any future deal with Iran.