The Institute for Science and International Security reported that new satellite images show the Iranian regime continues construction work at facilities located south of the Natanz uranium enrichment site, in a mountain known as Kolang. However, the precise nature of the nuclear-related activities at this facility remains unclear and is the subject of serious concern.
In its report published on Friday, October 3, the Institute added that these activities, observed since September 2025, appear to be in the final stages of construction and security reinforcement, and do not necessarily indicate an expansion or acceleration of nuclear activity.
The report emphasized that the analysis suggests these developments do not demonstrate a capability for the rapid reconstruction of damaged parts of the nuclear program.
The Washington Post also reported on Friday, September 28, citing satellite imagery and analysts’ assessments, that Iran’s regime continues to build a deeply buried military facility in the Kolang mountain area south of the Natanz nuclear site.
Turkey Freezes Assets of Individuals and Entities Linked to Tehran’s Nuclear Activities
This area has drawn increased attention from observers following U.S. and Israeli attacks.
The Washington Post report also emphasized that satellite imagery shows the Iranian regime has increased construction activity at the underground site in recent months.
This trend suggests that the Iranian regime has not completely halted work on its nuclear weapons program and is likely cautiously rebuilding lost capacities.
The project is being carried out at a site known as “Kolang Mountain,” where Iranian engineers have been tunneling into the Zagros Mountains since 2020, roughly 1.5 kilometers from Natanz.
Earlier, in May 2025, the Institute for Science and International Security reported that the Iranian regime was constructing a new security perimeter with additional fencing around Kolang-Gazla mountain.
Background and Current Status
The Institute for Science and International Security, which has monitored this site since construction began in late 2020, had previously noted the depth and scale of the tunnels, the reinforced entrances, and additional security measures such as walls and fences built around the mountain.
The report emphasized that as of June 2025, there was no evidence that these facilities had become operational, and recent activities confirm this assessment.
According to the Institute, one reason for the absence of a direct airstrike on this site during the 12-day conflict could be this assessment, though the possibility of unconventional attacks cannot be ruled out.
Eastern Entrance and Signs of Completed Excavation
The report also stated that satellite images from May to August show activity around the main eastern entrance of the tunnel—an entrance that has undergone the least stabilization work so far, with a continuous water flow suggesting possible geological problems in the area.
According to the Institute, the Iranian regime is now focusing on completing this entrance. The changing shapes of the excavated soil mounds indicate that the work is aimed more at completing structures rather than expanding the tunnel.
Reinforcement of 2007 Tunnel Facilities
According to the report, satellite imagery from August 10, 2025, provided by Maxar Technologies, shows that entrances to older tunnel facilities, built in 2007, have been reinforced with thick concrete and subsequently covered with soil. This measure is clearly intended to strengthen them against airstrikes or sabotage.
The complex had been inactive for years but has gradually been reactivated over the past five years, with significant changes in its security fencing and the construction of new entrance extensions in the past two years. Some of these extensions may serve as storage or support facilities for tunnel operations.
The report further notes that similar methods of reinforcing entrances were previously seen at the Fordow nuclear site, where, before the U.S. “Midnight Hammer” operation, air vents were protected with concrete walls.
The Iranian regime’s subsequent move to add similar reinforcements at Natanz raises the question of whether it managed to transfer valuable materials—including enriched uranium stockpiles or nuclear equipment—to these facilities before the U.S. strikes.
This concern intensified following June 18, 2025, satellite images showing a truck leaving the tunnel compound at around 9 a.m.
