High-resolution satellite images taken on September 11, 2026, showed continued construction and concrete fortification work at the entrances to the tunnel complex known as Jabal al-Fas, located south of Iran’s Natanz uranium-enrichment facility.
Construction changes and new access roads
A comparison of the latest images with footage from July 9 showed changes in several areas, including progress on surface structures and the presence of machinery and construction materials, as well as work near the tunnel entrances and roads leading to them. Work also advanced on a building in an area previously identified by the Institute for Science and International Security as a construction-support area linked to the tunnel project.
Concrete fortifications also appeared around one entrance after the institute documented concrete pouring and reinforcement work at several tunnel gates since February. The institute also observed rocks and soil being pushed and leveled over some entrance areas, saying the work aimed to increase protection and thicken the cover over parts of the entrances.
The complex’s location, names and reported functions
Tehran says the site is intended for assembling and manufacturing advanced centrifuges, while US and Israeli intelligence agencies suspect it could be a secret alternative uranium-enrichment facility. Experts say the complex is fortified against the most powerful US bunker-busting bombs.
The images coincided with remarks by US President Donald Trump on September 9, in which he said the United States had detected “some activity” at the site, warned Tehran against continuing it and threatened to strike the complex. The tunnel facility was not hit in strikes on other Iranian nuclear sites, despite its proximity to Natanz, which came under attack during the war.
