Iran’s secret underground nuclear site is busier than ever: Satellite images reveal major construction surge at Pickaxe Mountain amid US war

Satellite imagery has revealed a significant increase in construction activity at Iran’s heavily fortified Pickaxe Mountain site in 2026, as the conflict between the United States and Iran enters another tense phase.

A new analysis by the Center for Strategic and International Studies (CSIS), based on six years of satellite imagery, found that activity at the underground facility near Iran’s Natanz nuclear complex has reached its highest level since construction began.

The analysis suggests that work at the site has shifted from large-scale excavation towards internal construction and further reinforcement of the facility’s entrances and surrounding infrastructure.

What is Pickaxe Mountain and why is it important

Pickaxe Mountain, also known as Kuh-e Kolang Gaz La, is a deeply buried tunnel complex located around 2 km south of Iran’s Natanz uranium enrichment facility.

Construction began in 2020 after a fire at an above-ground centrifuge assembly facility at Natanz. Iranian officials had previously indicated that a larger and more modern centrifuge assembly facility would be built deep inside the mountain.

The International Atomic Energy Agency has sought information about the facility and requested access, but Iran has reportedly not granted those requests.

The exact purpose of the underground complex remains unclear. CSIS analysts have identified three possible uses — a centrifuge assembly facility, a uranium enrichment facility, or a site for other nuclear-related activities.

Satellite images show major construction surge

CSIS researchers examined imagery from 2020 onwards using synthetic aperture radar, optical satellite imagery and very-high-resolution commercial images.

Their analysis identified a clear change in activity during 2026. The facility has recorded more road activity this year than at any previous point in its construction history.

The work includes strengthening and raising tunnel entrances, paving internal roads, reinforcing areas around the portals and removing piles of material excavated during earlier tunnelling.

The imagery indicates that the project may now be moving from the excavation stage towards construction inside the underground complex, although exterior reinforcement is continuing.

Does Iran have centrifuges inside Pickaxe Mountain

There have been reports that Iran may have moved centrifuges or centrifuge components into the facility.

However, the latest CSIS analysis does not confirm or disprove those claims.

Researchers said the continuing construction activity, along with the absence of an increased security presence and specialised non-construction equipment, suggests the facility may not yet be operational for uranium enrichment, if that is ultimately its intended purpose.

This distinction is important because satellite imagery can reveal construction patterns and changes around the site, but it cannot by itself establish what equipment or activities are taking place deep underground.

Why the underground facility is difficult to attack

Pickaxe Mountain is buried deep beneath granite, making it a particularly challenging military target.

CSIS analysts said even the United States' heaviest non-nuclear bunker-busting weapon, the GBU-57 Massive Ordnance Penetrator, may face difficulties against such a deeply buried facility.

The site's tunnel entrances have also been designed with bends that could reduce the ability of blasts or missiles to travel directly into the underground complex.

US President Donald Trump has previously threatened to strike the facility, saying Washington could target Pickaxe Mountain as the conflict with Iran escalates.

US explores ways to strike deeply buried targets

The United States has also been examining ways to attack deeply buried underground facilities.

According to the report, an emergency contract was issued before the launch of Operation Epic Fury to repair a specialised underground testing facility at the White Sands Missile Range in New Mexico.

The facility is used to study the effects of weapons against deeply buried targets. Sources cited by CNN said the work was linked to efforts to develop ways of targeting Iran's deepest underground facilities, although the precise details could not be independently verified.

Satellite imagery also showed excavation activity at the White Sands site beginning in February before the work appeared to stop in March.

US developing next-generation penetrator

The challenge of striking deeply buried Iranian facilities has also prompted the US military to pursue a new generation of penetrator weapons.

The US previously used its Massive Ordnance Penetrator bombs during Operation Midnight Hammer, which targeted Iranian nuclear facilities in June 2025.

However, a senior US general later told lawmakers that the deeply buried Isfahan facility had largely been attacked at its entrances because the Pentagon believed existing bunker-busting weapons might not be capable of destroying the facility itself.

The US Air Force is now pursuing development of a next-generation penetrator intended to reach targets buried deeper underground.

Pickaxe Mountain remains under intense scrutiny

The renewed activity at Pickaxe Mountain comes as the wider US-Iran conflict has entered another period of escalation.

The underground facility is particularly significant because it is one of the major elements of Iran's nuclear infrastructure that has not been directly struck, while construction has continued despite previous attacks elsewhere.

For now, satellite imagery points to a major increase in activity but does not establish that uranium enrichment is taking place inside the mountain.

CSIS researchers said the imagery provides evidence of a transition towards a more advanced stage of construction, while the ultimate purpose and operational status of the underground facility remain uncertain.


Inputs from TOI