Is Iran rebuilding its nuclear programme at Pickaxe Mountain?

Iran's heavily fortified Pickaxe Mountain is one of the most closely monitored locations in the country's nuclear programme, following intelligence assessments that Tehran has transferred thousands of uranium enrichment centrifuges into the underground complex after its nuclear infrastructure suffered extensive damage in June 2025.

United States and Israeli officials have said Iran relocated sensitive nuclear equipment there in an apparent effort to preserve its enrichment capabilities from future military strikes, reported the Wall Street Journal on Monday.

The developments come as tensions between Washington and Tehran continue to escalate, with US President Donald Trump threatening military action against the underground facility while international inspectors remain unable to verify exactly what is taking place inside the mountain.

Located a short distance from the Natanz nuclear complex, it known as Pickaxe Mountain or Kuh-e Kolang Gaz Sere.

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Satellite imagery analysis shows continuous engineering work, reinforced tunnel entrances and extensive construction activity beneath one of Iran's most protected mountain formations.

Although Iranian authorities maintain that the underground complex is intended only for manufacturing and assembling advanced centrifuges, international inspectors have been unable to independently verify activities taking place inside the mountain.

Why do we know about Pickaxe Mountain?

The attention on Pickaxe Mountain stems largely from what happened after the June conflict last year between Iran and the US-Israel.

During the 12-day war, American and Israeli forces carried out extensive strikes against Iran's nuclear infrastructure in an operation known by the United States as "Operation Midnight Hammer."

Three of Iran's principal nuclear sites were targeted during the campaign, including facilities at Natanz, Fordow and Isfahan, causing extensive damage to infrastructure associated with Tehran's uranium enrichment programme.

Natanz, regarded as the centrepiece of Iran's uranium enrichment activities, suffered particularly significant damage. Before the attacks, the complex housed two enrichment facilities — one located above ground and another buried underground.

According to the International Atomic Energy Agency (IAEA), the above-ground enrichment plant was destroyed, while the underground facility was believed to have sustained at least substantial damage during the military operations.

According to intelligence assessments shared by Israeli officials with Washington, Tehran responded by relocating surviving elements of its enrichment infrastructure to locations considered significantly more secure.

Among the most significant reported moves was the transfer of thousands of advanced uranium enrichment centrifuges into the underground tunnel network beneath Pickaxe Mountain during the second half of 2025.

Officials from both the United States and Israel believe the relocation was intended to ensure that Iran would retain the ability to continue uranium enrichment even if additional military campaigns were to destroy other facilities.

Unlike Natanz, Fordow and Isfahan, the tunnel complex beneath Pickaxe Mountain was not struck during either the June 2025 war or the subsequent military operations that followed.

The Institute for Science and International Security (ISIS), a Washington-based think tank specialising in nuclear non-proliferation, has noted that the underground facility remained untouched despite repeated attacks elsewhere on Iran's nuclear infrastructure.

According to assessments cited by nuclear non-proliferation experts, between 400 and 450 kilograms of uranium enriched to 60 per cent survived previous military operations and has not been publicly accounted for.

Experts at ISIS have identified Pickaxe Mountain as one of the most likely locations where such material could potentially be stored securely or preserved for future use, although no independent verification has been possible because inspectors have not been granted access to the underground complex.

How is Pickaxe strategically located?

Pickaxe Mountain is situated approximately two kilometres south of the Natanz nuclear complex in central Iran and around 220 kilometres south of Tehran.

Although it lies close to one of Iran's best-known nuclear facilities, the underground complex itself occupies an entirely different level of physical protection.

The mountain reaches an elevation of roughly 1,600 metres above sea level, making it substantially larger than the mountain sheltering Iran's Fordow enrichment facility, which stands at approximately 960 metres.

The importance of the location became apparent following events in 2020.

Construction of the underground complex began after an explosion destroyed Natanz's above-ground centrifuge assembly hall in what Iranian authorities described at the time as an act of sabotage.

The blast caused extensive damage that Iran said would slow development of advanced uranium enrichment centrifuges.

In response, Tehran announced plans to construct an entirely new underground facility within the mountain itself.

In September 2020, Iran's then nuclear chief Ali Akbar Salehi disclosed that the country had begun building "a more modern, larger and more comprehensive hall in all dimensions in the heart of the mountain near Natanz" dedicated to manufacturing advanced centrifuges.

That announcement marked the public beginning of what has since become one of Iran's most heavily protected nuclear-related construction projects.

According to the Institute for Science and International Security, excavation work gradually created an extensive tunnel system running deep beneath solid granite rock.

Satellite imagery shows that the complex contains two pairs of tunnel entrances — one eastern pair and one western pair — which are believed to provide access to a single large underground facility.

The site's overall layout differs noticeably from Fordow. Where Fordow relies primarily on two access portals, Pickaxe Mountain features four major tunnel entrances distributed across the mountain.

Analysts believe this design provides greater logistical flexibility while also complicating efforts to disable the facility through attacks aimed solely at blocking entrances.

Available satellite analysis suggests the principal underground halls are located between approximately 90 metres and more than 137 metres beneath solid granite, with several assessments indicating portions of the complex extend beyond 100 metres below bedrock.

This makes Pickaxe Mountain deeper than Fordow, whose underground chambers are generally estimated to lie between 80 and 90 metres beneath the mountain.

For military planners, those additional metres represent a major operational challenge. Granite is among the hardest naturally occurring rocks, meaning that penetrating to such depths would require considerably more force than striking facilities protected by softer geological formations.

Even the United States' most powerful bunker-penetrating bomb, the GBU-57 Massive Ordnance Penetrator (MOP), is widely considered unlikely to reliably destroy the deepest chambers beneath the mountain using conventional aerial attacks alone.

According to ISIS, security arrangements include an extensive protective perimeter around the complex together with reinforced tunnel entrances designed to increase resistance against potential attacks.

Recent satellite imagery has also shown that the eastern tunnel portals have been partially backfilled since the wars. According to ISIS, these entrances have been obstructed to restrict ground vehicle access, although they have not been completely sealed.

Meanwhile, additional defensive work has continued around the western portals.

Satellite imagery indicates substantial concrete reinforcement around the western entrance extensions, together with the addition of thick earth and rock coverings intended to absorb explosive force.

Analysts have also observed that older tunnel systems dating back to around 2007 near the base of the mountain have now been buried and reinforced.

The apparent sealing of those legacy tunnels has led experts to conclude that equipment or other sensitive materials may have been relocated into newer underground sections before the older passages were closed.

Satellite images have recorded the regular presence of dump trucks, cranes, cement mixers and other heavy engineering equipment operating around the tunnel entrances this year.

Covered logistics vehicles have also been observed entering and leaving the complex, indicating that work beneath the mountain has continued despite the wider military conflict.

What has the IAEA said?

The United Nations nuclear watchdog International Atomic Energy Agency (IAEA) has repeatedly sought access to the underground site, but Iranian authorities have continued to deny inspectors entry.

According to the IAEA, Iran had informed the agency as early as 2021 that nuclear-related activities were planned at the mountain.

Yet officials say Tehran has not supplied sufficient information to allow inspectors either to verify those declarations or to exclude the possibility that nuclear material is present inside the underground halls.

IAEA Director-General Rafael Grossi has repeatedly sought clarification from Iran regarding activities taking place at the site.

Speaking earlier this year, Grossi observed that Tehran's decision to expand underground facilities was part of a broader long-term strategy. "This was part of their quite systematic intention to put their most sensitive facilities underground," he said.

While Grossi acknowledged that Iran had previously declared its intention to undertake nuclear-related work at Pickaxe Mountain, he also noted that the lack of present-day access leaves inspectors unable to independently examine the underground complex.

As a result, satellite imagery has become one of the principal tools available for monitoring developments.

The Institute for Science and International Security has assessed that although construction continues, the underground complex itself has not yet become operational as a functioning enrichment cascade facility.

Its report states, "It is also unclear if Iran still plans on installing a large-scale assembly facility, given the destruction of Iran’s centrifuge program, including Iran’s ability to make centrifuge components needed for an assembly plant.

"Nonetheless, if Iran starts to rebuild its centrifuge manufacturing capability, it could plan to install a smaller centrifuge assembly facility in Pickaxe Mountain able to serve a nuclear weapons program."

How can the issue be addressed?

The mountain's geology, engineering and depth have combined to make it one of the most heavily protected nuclear-related locations known to exist.

Current assessments suggest that conventional air-delivered bunker-buster bombs are unlikely to penetrate deeply enough to destroy the principal underground chambers.

As a result, military planners have examined alternative approaches should the site ever become a target. Rather than attempting to collapse the underground halls directly, analysts believe operations could instead focus on disabling access to the facility.

Possible methods discussed by defence experts include collapsing the four principal tunnel entrances, cutting external electricity supplies, severing ventilation systems or carrying out specialised ground operations designed to sabotage underground infrastructure.

Foreign Policy Research Institute fellow Sam Lair, after reviewing recent satellite imagery, said increasing the resilience of tunnel entrances would complicate any attempt to strike them using penetrating weapons.

He told Reuters that strengthening the entrances would complicate "targeting with penetrating munitions like bunker busters".

Lair also observed, "We can infer that there are ongoing activities at Pickaxe Mountain the Iranians wish to continue but are still concerned enough about a potential attack that they are taking steps to bolster their defenses."

Even if military action were eventually taken, another challenge would remain. Without inspectors or personnel on the ground, verifying precisely what damage had been inflicted inside the mountain would be extremely difficult.

What has Donald Trump said?

As military tensions continue between Washington and Tehran, during an interview on the Hugh Hewitt Show, Trump openly warned that the underground facility could become a future military target.

"We're going to take out Pickaxe Mountain. Tell the Iranians to be ready," Trump said.

In the same interview, he suggested that Washington was closely monitoring developments at the site. "We're watching (Pickaxe Mountain) closely. We see no activity there. They're not doing well with their nuclear situation. Every time we hear about it, we blow it up. So they don't like talking about it. But we'll probably give Pickaxe a shot relatively soon," Trump said.

In another interview, Trump repeated that the administration continued to monitor the underground complex. "We're watching Pickaxe Mountain very closely... Pickaxe is a possible target for a nice, big, fat shot right near the front door."

His comments came as Washington announced that it was reinstating its blockade of Iranian shipping in the Gulf and said it would ensure that the Strait of Hormuz remained open — for a fee — following renewed exchanges of missiles and drones between the United States and Iran.

Trump also issued a broader warning regarding military operations against Iran.

"We're going to hit them very hard tonight and we're going to hit them hard tomorrow. And there's not a damn thing they can do about it," he said during the interview.

Although intelligence agencies, nuclear inspectors and defence analysts differ on several aspects of the facility's present operational status, there is broad agreement on two points.

First, the underground complex has become one of the most heavily fortified locations associated with Iran's nuclear infrastructure. Second, the absence of independent access means many critical questions remain unanswered.

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With inputs from agencies