Iran’s Mount Fass: A Nuclear Stronghold Deeper Than Fordo and Natanz

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Despite U.S. President Donald Trump’s announcement of the destruction of Iran’s Fordo nuclear facility, Western concerns are mounting over a potential shift of Iran’s nuclear core operations to a secret mountain fortress known as “Mount Fass.”

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Located about 145 kilometers south of the Fordo facility and very close to the Natanz nuclear site in Isfahan province, central Iran, “Mount Fass” — locally called “Kuh Kolang Gaz La” — is believed to be a deeply buried underground nuclear site, according to The Sun.

The site reportedly features massive tunnels and four main entrances — two on the eastern side and two on the western side — each measuring about six meters wide and eight meters high. The facility is estimated to be 100 meters underground, making it far more secure and protected than Fordo or Natanz.

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Over the past four years, the installation has been secretly expanded and reinforced. Satellite imagery reveals a complex network of tunnels leading to hidden facilities deep beneath the mountain.

Experts believe this location could serve as a safe haven for enriched uranium allegedly smuggled out of Fordo ahead of the recent U.S.-Israeli airstrikes. Reports indicate that approximately 400 kilograms of uranium enriched to 60% — enough to build several nuclear warheads — are currently unaccounted for.

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Rafael Grossi, Director General of the International Atomic Energy Agency (IAEA), has stated that Iran refused to disclose details about activities at Mount Fass, telling him, “That’s none of your business.” Nevertheless, he confirmed that the existence of secret nuclear operations and undeclared stockpiles underground cannot be ruled out.

This new site has triggered serious international concern, as its depth makes it nearly unreachable by American bunker-buster bombs such as the GBU-57, which were used in the recent strikes.

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The facility reflects Iran’s broader strategy of shielding its nuclear program from airstrikes by relocating vital operations to heavily fortified underground locations. Mount Fass is reportedly equipped with advanced security systems and guarded by Iran’s Islamic Revolutionary Guard Corps, further complicating any potential military action.

In the days leading up to the U.S. strikes, movements of trucks carrying sensitive materials were observed near Fordo, suggesting a possible relocation to Mount Fass.

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Experts fear that this site could become a central hub for nuclear development and storage, allowing Iran to continue its nuclear activities despite air raids aimed at dismantling its program.

Mount Fass thus poses a significant challenge to global non-proliferation efforts. It complicates the monitoring of Iran’s nuclear activities, particularly as Tehran continues to restrict access for IAEA inspectors.

Iran is expected to further fortify and develop the site, prompting the international community to consider new strategies for oversight and containment of Iran’s nuclear ambitions.

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