The United Nations' nuclear watchdog has confirmed what inspectors long suspected but could never prove: the government of ousted Syrian president Bashar al-Assad secretly built a nuclear reactor in the eastern desert and stockpiled dozens of tons of undeclared uranium, in violation of Syria's international nonproliferation commitments.

In a confidential report circulated to member states this week, the International Atomic Energy Agency said it has now "clarified and resolved" the outstanding questions of an investigation that began after Israel bombed a suspected reactor site at Deir al-Zour in 2007. Inspectors found that the facility's cooling infrastructure was "consistent with that of a nuclear reactor," and identified a connected fuel fabrication plant and a storage site where nuclear material, uranium scrap and waste had been kept.

The agency said it uncovered roughly 73 metric tons of undeclared natural uranium metal, with about 55 tons in the form of fuel rods manufactured domestically inside Syria — far more material than had previously been documented. The IAEA first detected uranium particles at the site during sampling in 2024; a verification visit late last month, following months of on-the-ground access, allowed inspectors to finally piece together the full picture.

A cold case reopened by regime change

Damascus had stonewalled IAEA questions about Deir al-Zour for nearly two decades. After Israel's 2007 airstrike destroyed the partially built reactor — reportedly constructed with North Korean assistance — Assad's government bulldozed the site and largely refused to answer the agency's follow-up inquiries, leaving the file open even as Syria descended into civil war.

That changed after Assad was toppled in December 2024. Syria's new authorities, led by transitional leadership that has sought to rehabilitate the country's international standing, granted IAEA inspectors access to the site and related facilities. Agency Director-General Rafael Grossi met Syrian Foreign Minister Asaad al-Shibani in August as part of the renewed cooperation. The IAEA said all the recovered nuclear material now remains under its containment and surveillance, and that Syria's new government has committed to keeping it inside the country while expressing interest in eventually pursuing a civilian nuclear energy program under international safeguards.

The agency, having received the necessary information and access from Syria, has been able to clarify and resolve its outstanding questions.

The report is a rare instance of an old nonproliferation file being closed through cooperation rather than confrontation, and it stands in sharp contrast to the IAEA's parallel investigation into Iran, where the same report found no progress: inspectors still cannot access Iranian sites struck by the United States and Israel in June 2025, and the agency says it lacks clarity on Tehran's remaining stock of highly enriched uranium, previously estimated at more than 440 kilograms — enough, if further enriched, for roughly ten weapons.

Nonproliferation analysts say the Syria findings close one of the longest-running mysteries in the IAEA's history and hand Damascus's new government a diplomatic win as it works to shed the pariah status of the Assad era. Attention now turns to whether the agency's Board of Governors will use its findings to formally declare Syria in past noncompliance, and to how the recovered uranium stockpile will ultimately be disposed of or secured for the long term.