Iran has been reinforcing an underground complex carved into a mountain near one of its most sensitive nuclear facilities, according to newly analysed satellite imagery, raising fresh questions about Tehran’s intentions at a time of escalating tensions with the United States.
The images, first assessed by the Washington-based think tank Institute for Science and International Security (ISIS), show significant construction activity at Mount Kolang Gaz La, also known as Pickaxe Mountain, situated close to Iran’s Natanz nuclear facility. Analysts say the work appears aimed at strengthening tunnel entrances and enhancing protection against potential air strikes.
The developments come as diplomatic efforts between Tehran and Washington continue amid renewed threats from US President Donald Trump, who has warned of possible military action if Iran does not agree to a new nuclear agreement.
A satellite image dated 10 February shows what appears to be freshly poured concrete covering one of the tunnel entrance areas at Pickaxe Mountain. A boom pump used for delivering concrete is visible at the site, according to analysts from ISIS and the UK-based intelligence firm Maiar.
At another entrance, rock and soil appear to have been pushed back and flattened, while a new concrete-reinforced structure stands nearby. Experts suggest the changes are consistent with fortification efforts designed to shield the facility from aerial bombardment or sabotage.
“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,” ISIS said in its assessment.
Although Iranian officials have previously linked construction at the site to rebuilding an advanced centrifuge assembly plant, the scale of the work and the depth of the tunnels have fuelled speculation that more critical nuclear-related operations could eventually be housed there.
ISIS noted that the continued presence of heavy machinery and construction materials indicates the facility is unlikely to be fully operational at present.
Pickaxe Mountain was not among the locations targeted during US and Israeli air strikes in June 2025. However, the nearby Natanz nuclear facility — located roughly 2 km to the north — was hit during those operations.
The strikes came amid a 12-day war between Israel and Iran, during which the United States joined Israel in attacking underground nuclear facilities where centrifuges were reportedly enriching uranium to high levels.
President Trump declared at the time that the strikes had “obliterated” Iran’s enrichment capacity. However, he later warned that Iranian officials were considering establishing a new site, claiming that Tehran had been as little as a month away from producing a nuclear weapon.
Iran has consistently denied that it seeks to develop nuclear arms, insisting that its nuclear programme is entirely peaceful and intended for civilian energy and research purposes.
Still, Western governments and nuclear watchdogs have raised alarms about the scale and level of uranium enrichment achieved by Iran in recent years.
Satellite images also show signs of reconstruction and fortification at other major nuclear sites, including Natanz and the Isfahan nuclear complex, located about 125 km to the north.
At Isfahan, satellite imagery reviewed by ISIS reveals that all entrances to its tunnel complex appear to have been sealed with earth. Analysts say such “backfilling” can help dampen the impact of air strikes and complicate efforts to seize or destroy sensitive materials stored underground.
The Isfahan site also features a newly constructed roof on a building previously damaged in an Israeli strike last year. The structure is believed to have been used for centrifuge manufacturing — a critical component of uranium enrichment.
Meanwhile, above-ground repairs are visible at Natanz, where a damaged anti-drone cage at an enrichment plant has been covered with a newly built roof between early December and January. ISIS assessed that the roof may have been added to obstruct aerial observation of activities beneath it.
The pattern of repairs and fortifications across multiple facilities suggests a coordinated effort to harden Iran’s nuclear infrastructure against further attacks.
Prof. Sina Azodi, director of the Middle East Studies Program at George Washington University, said the construction reflects Tehran’s expectation of continued hostilities.
“Iran is operating under the assumption that the attacks are going to happen and they need to protect the facilities as much as they can,” he said.
Azodi argued that despite the strikes last year, Iran’s nuclear expertise and technological capabilities remain intact.
“The Iranian nuclear programme hasn’t been destroyed,” he said. “Clearly once you have the knowledge and capacity and technology to reconstruct the programme, you can always rebuild everything.”
That assessment underscores a central dilemma for policymakers in Washington and Tel Aviv: while military strikes can damage physical infrastructure, they cannot eliminate scientific knowledge or technical expertise.
One of the most pressing concerns involves Iran’s stockpile of highly enriched uranium (HEU). According to estimates cited by international officials, Iran possesses roughly 400 kg of HEU enriched to levels just short of weapons-grade — a threshold that would require only a short additional technical step to convert into material suitable for a nuclear weapon.
Rafael Grossi, head of the global nuclear watchdog, the International Atomic Energy Agency (IAEA), said he believes the material remains stored in underground tunnels and chambers, including sites targeted by US bunker-busting bombs last June.
Grossi, speaking at the Munich Security Conference, said there remains a narrow window for a new diplomatic agreement between Iran and the United States.
“My sense, talking to all those involved, is that we have a window of opportunity, but windows of opportunity have a tendency to shut themselves quite abruptly and brusquely,” he said. “We need to seize the moment.”
The IAEA has long sought greater transparency and access to Iranian facilities. While inspectors continue to monitor certain declared sites, access has been constrained in recent years following Tehran’s scaling back of cooperation in response to US sanctions and political disputes.
The renewed construction at Pickaxe Mountain comes amid ongoing negotiations aimed at crafting a successor to the 2015 nuclear agreement, which limited Iran’s enrichment activities in exchange for sanctions relief.
President Trump withdrew the United States from that deal during his first term, arguing that it failed to address Iran’s ballistic missile programme and regional activities. Since then, Iran has progressively expanded its enrichment activities, installing advanced centrifuges and increasing stockpiles of enriched uranium.
The latest diplomatic efforts seek to curb those activities once again, but mistrust remains deep on both sides. Trump’s recent remarks threatening military action if talks fail have heightened tensions and raised concerns among European allies.
Iranian officials have responded by reiterating their position that the country’s nuclear programme is peaceful and compliant with its interpretation of international obligations. They have also warned that further military strikes would provoke retaliation.
The fortification of underground facilities reflects lessons learned from previous attacks. By building deeper tunnels, reinforcing entrances with concrete, and sealing access points, Iran appears intent on making any future strike more costly and less effective.
Military analysts note that while bunker-busting bombs can penetrate significant depths, their effectiveness depends on accurate intelligence about tunnel layouts and the precise location of sensitive equipment.
If Iran succeeds in relocating key elements of its enrichment infrastructure into more heavily fortified or undisclosed locations, it could complicate any attempt to neutralise the programme through force.
At the same time, the visibility of construction activity in satellite imagery suggests that Tehran is not attempting to conceal the existence of the site entirely. Some analysts interpret this as a signal — a demonstration of resilience and defiance in the face of external pressure.
As satellite imagery continues to reveal activity at Pickaxe Mountain, Natanz and Isfahan, the broader trajectory of Iran’s nuclear programme remains uncertain.
The interplay between diplomacy and deterrence will likely determine whether the current fortification efforts serve as a prelude to renewed confrontation or a bargaining chip in negotiations.
For now, the reinforced tunnel entrances at Pickaxe Mountain stand as a stark reminder that Iran’s nuclear infrastructure — far from being dismantled — is adapting to survive in an era of heightened scrutiny and recurring threats of force.
Whether diplomatic efforts can outpace the construction work in the mountains of central Iran remains one of the most consequential questions facing the international community.
