High-resolution satellite imagery of Iran’s largest and most crucial remaining nuclear facility shows a recent rush to protect it from potential US or Israeli aerial attack, according to the Institute for Science and International Security (the “good ISIS”).
Satellite imagery on Tuesday appeared to show that Tehran has taken advantage of delays in any such attack since the December 28 protests started to better defend the facility.
The nuclear facility in question is a large tunnel complex at Kuh-e Kolang Gaz La, aka Pickaxe Mountain. It is near a series of Natanz nuclear facilities that were the center of the Islamic Republic’s nuclear program until the 12-day war between Israel and Iran last June.
Most of the other numerous Natanz facilities, including existing centrifuges at the time, were destroyed in the conflict. For reasons that have not been fully explained, this facility was not struck.
Construction at the site started by 2021, and the ISIS think tank and The Jerusalem Post revealed its existence to the public in early 2022.
According to the think tank, the relatively new, enormous underground facility is still not thought to be operational, one of the reasons it may not have been struck previously. But there are concerns that it could be used to enrich uranium or even for some kind of clandestine rush to a small nuclear weapon at some point if not dealt with.
Tehran continues to invest in its most important undamaged nuclear facility
Since last June, it almost certainly has received extra attention and emphasis from Iran as its singularly most important undamaged facility for potential nuclear program use.
From the start, Iran had been digging and building this new facility near the Natanz area very deep under the mountain, which is far larger than the one atop the Fordow facility and would be even more impregnable. The US bombed Fordow with bunker busters last June.
The main mountain harboring the new Natanz tunnel complex is 1,608 meters above sea level, the think tank said.
The mountain that harbored the Fordow centrifuge enrichment plant, called Kūh-e Dāgh Ghū’ī, was about 960 meters tall.
This makes the Natanz mountain about 650 meters taller, or more than 50%, potentially providing even greater protection to any facility built underneath it.
All this was true even before last June.
Heavy construction suggests facility is not yet ready for operations
In a previous report, ISIS president David Albright wrote: “Fordow is already viewed as so deeply buried that it would be difficult to destroy via aerial attack. The new Natanz site may be even harder to destroy.”
There are “ongoing efforts to harden and defensively strengthen two of the tunnel entrances into the facility,” the think tank said in its latest report. “Imagery shows ongoing activity throughout the complex related to this effort, involving the movement of numerous vehicles, including dump trucks, cement mixers, and other heavy equipment like backhoes and truck-mounted cranes.”
“As of February 10, concrete is being poured on top of the Western tunnel entrance extension,” the report said. “At one of the eastern tunnel entrances, rock and soil can be seen pushed back and leveled on top of the tunnel portal. Additionally, over the last month, a concrete-reinforced headworks for the tunnel entrance extension was added. This allows for additional overburden in the form of additional rock, soil, or concrete.”
“These efforts strengthen the tunnel portals and provide additional protection against an airstrike,” the report added. “Nearby the eastern tunnel portals, piles of construction materials can be seen on the ground.”
“The ongoing presence of heavy construction machinery and materials around the site indicate that the facility is likely not yet ready for operations, however, over the last two months, smaller vehicles and closed-roof vehicles have also been observed near the entrances, indicating that Iran may be in the process of outfitting the interior of the tunnel complex,” the ISIS report said.
Moreover, “In the past, Iran has tied the construction to rebuilding an advanced centrifuge assembly plant, but the size of the facility, as well as the protection provided by the tall mountain, raised immediate concern whether additional sensitive activities are planned, such as uranium enrichment,” it said. “Whether the current levels of visible utility support in the form of one probable ventilation shaft with above- and below-ground power lines are sufficient to support such operations inside the tunnel seems doubtful.”
Accordingly, Israel can hope that the facility may not be capable of all of the nuclear activities Iran lost when its main facilities at Natanz, Fordow, and Isfahan were heavily damaged in June 2025.
But if Tehran is planning to expand the facility’s capabilities, the last two months of work covering its potential vulnerabilities have made an already extremely difficult target to hit even more difficult.