Iran Accelerates Secret Underground Nuclear Facility Construction, CNN Reports

Iran has significantly ramped up construction at a secret underground nuclear facility located beneath "Pickaxe Mountain," according to an analysis of satellite imagery by the Center for Strategic and International Studies (CSIS). The findings, revealed by CNN on September 9, indicate a "clear surge in construction activity" in 2026 at the site, situated about 1.5 kilometers from the Natanz nuclear complex. Construction on the facility, which began in 2020, has long been a source of intelligence concern due to its unclear purpose. Theories suggest it could be intended to house advanced uranium enrichment centrifuges, protecting them from airstrikes, or to be used for the final assembly of nuclear weapons.

CSIS analysts believe Iran has likely completed the main tunneling phase and is now focusing on internal outfitting and reinforcing external infrastructure. Satellite images show increased road paving, tunnel entrance improvements, and debris removal, with road traffic to the site reaching record levels this year. However, the ongoing construction suggests the facility may not yet be ready for uranium enrichment, if that is its intended use. CSIS assesses the underground complex is likely designed as a protected haven for Iran's nuclear program, potentially for centrifuge assembly, enrichment, or other weapons-related activities, including the production of metallic uranium.

Israeli intelligence suggests Iran may have already transferred thousands of uranium enrichment centrifuges to the Pickaxe Mountain tunnels in the fall of 2025, following a recent conflict. This intelligence has been shared with the United States. The granite mountain is believed to offer protection even from powerful U.S. bunker-buster bombs, which have had limited success against deeply buried Iranian nuclear sites, such as the one in Isfahan. U.S. President Donald Trump recently reiterated threats to strike the facility, stating, "We know about everyone moving around there."

The U.S. military has developed operational plans for an attack on Pickaxe Mountain, but concerns remain about the ability of current munitions to penetrate deep enough to destroy any equipment inside. The Pentagon is reportedly exploring options for "decisive strikes" on such hardened targets. This effort is indirectly supported by activity at the White Sands Missile Range in New Mexico, where a unique underground test facility was prepared in February 2026 for a "combat test" to address rapidly emerging threats, potentially related to striking deeply buried Iranian nuclear sites. CNN could not independently verify the test's occurrence or purpose, and the Pentagon did not respond to inquiries. Meanwhile, the U.S. is developing a next-generation bunker-buster bomb to counter deeper threats, with a prototype contract awarded in September 2025.

Separately, Iran's exact location of highly enriched uranium remains unknown. The country possesses approximately 440 kg of uranium enriched to 60%, with the capability to quickly reach weapons-grade 90%. The IAEA Director General Rafael Grossi estimates at least half of these reserves are located beneath rubble in Isfahan, with other stockpiles possibly at Fordow and Natanz. Some of this material may have been moved to the Pickaxe Mountain tunnels.