AL-MUKALLA: Between June 13 and 24 last year, Israel and the US launched a series of attacks designed to cripple Iran’s nuclear program.

The target list included the Natanz and Fordow enrichment plants, the Isfahan Nuclear Technology Center, an under-construction heavy-water reactor at Arak, and dozens of other sites, including centrifuge-production facilities, laboratories and research centers.

On June 25, four days after American aircraft and missiles struck Fordow, Natanz and Isfahan, US President Donald Trump hailed the operation as having inflicted extensive damage on Iran’s nuclear infrastructure.

But one site was conspicuous by its absence from the lists of targets struck by Israel’s Operation Rising and America’s Operation Midnight Hammer: the nuclear facility known as Pickaxe Mountain. Now, however, it might finally be in Washington’s crosshairs.

The mountain — called Kuh-e Kolang Gaz La in Farsi — lies just south of the Natanz complex that was badly damaged last year. Recent satellite imagery appears to confirm earlier reports of intensified activity at the site, suggesting Iran might be putting in place defenses designed to protect the area against airstrikes.

Joseph Rodgers, deputy director of the Project on Nuclear Issues at the Center for Strategic and International Studies, told Arab News that construction work at Pickaxe had accelerated sharply since Operation Midnight Hammer, and was now at its highest level in the history of the site.

About a year ago, satellite analysis commissioned by The Washington Post revealed activity at the underground site that suggested Tehran might have been cautiously rebuilding elements of its nuclear infrastructure.

International nuclear inspectors have never visited the facility and its purpose remains unclear. When work began at the site in 2020, Iran said it was intended to house a plant for manufacturing the centrifuges used in uranium enrichment. Since then, concerns have grown that it could also serve as a secure storage facility for near-weapons-grade enriched uranium or other sensitive nuclear material.

Rodgers said Israeli intelligence had claimed Iranian authorities moved centrifuges into Pickaxe Mountain last fall. This provided circumstantial evidence that Tehran could be considering expanded activity at the site, he added, including enrichment or additional nuclear research.

One reason Pickaxe might not have been attacked last year was its depth. Analysts estimate that parts of the facility are buried between 80 and 100 meters beneath a granite mountain, potentially deeper than Fordow and beyond the effective reach of even the most powerful conventional, earth-penetrating weapons in the US arsenal.

Behnam Ben Taleblu, senior director of the Iran Program at the Foundation for Defense of Democracies, has argued that the opportunity to destroy the site might already have narrowed, because the facility is buried significantly deeper than Fordow. He also suggested that the US could instead attempt to target and seal the entrances, making it difficult and costly for Iran to restore access.

The site has been on Washington’s radar for months and Trump has repeatedly threatened to attack it. In July, he publicly identified Pickaxe Mountain as a possible target, and later said Iran might have moved centrifuges into the underground complex. He also linked the fate of the facility to negotiations with Tehran, warning that the US could strike it if no agreement was reached.

The issue has returned to prominence ahead of the visit by the Iranian president and foreign minister to New York next week for the UN General Assembly.

It also coincides with analysis of recent satellite imagery from Pickaxe Mountain. The Institute for Science and International Security said images captured on Sept. 11 showed Iran had added a series of earthen barriers across roads leading to western tunnel entrances in late July and early August. The institute assessed that the barriers were probably defensive measures intended to restrict rapid access to and from the tunnel portals.

Trump has also returned publicly to the issue, warning this month that renewed activity at the site could trigger further US military action. His remarks coincided with the publication of an analysis by the Center for Strategic and International Studies of satellite images collected since 2020. The think tank said the imagery revealed more road activity at Pickaxe Mountain in 2026 than at any time in the site’s history. It identified a clear surge in construction, including hardened tunnel-access points, paved internal roads, reinforcement around entrances and the removal of excavation debris.

The International Atomic Energy Agency has repeatedly sought information about, and access to, Pickaxe Mountain but the site has yet to be inspected.

The Iranian president, Masoud Pezeshkian, previously dismissed satellite imagery as inconclusive and said international inspectors could clarify the site’s purpose on the ground. However, Tehran has imposed restrictions on inspectors, complicating efforts to independently establish what is going on inside the facility.

The Center for Strategic and International Studies has identified at least three possible explanations for the construction inside Pickaxe Mountain: Iran could be constructing the centrifuge-assembly facility it announced in 2020; it could be developing a uranium-enrichment facility capable of processing its existing stockpile of highly enriched uranium; or nuclear-related research previously conducted at facilities damaged by US and Israeli attacks could have been moved there.

In any case, Washington’s military options for seriously damaging the facility might be limited. Rodgers told Arab News that its estimated depth of up to 100 meters inside granite potentially placed it beyond the reach of the US military’s most sophisticated bunker-busting weapon, the GBU-57 Massive Ordnance Penetrator.

The GBU-57, carried by the B-2 stealth bomber, is the largest conventional bunker-busting weapon in the US arsenal. The 30,000-pound precision-guided munition carries a 5,000-pound explosive warhead and is designed to penetrate deeply buried and hardened targets.

Fordow, though also buried deep underground, had structural vulnerabilities that could be exploited during an attack. Pickaxe presents a different challenge altogether.

A Center for Strategic and International Studies analysis indicated that Iran continued construction at the mountain immediately after Operation Midnight Hammer last year. Between June and September 2025, Iran completed a security perimeter around the facility, reinforced several tunnel entrances and accelerated excavation work.

The design of the complex might further complicate any future attack. The center said the tunnel approaches appeared to feature U-shaped bends, which could prevent missiles from traveling directly along underground corridors and reduce the ability of blast waves to penetrate deep into the mountain.

Rodgers said the broader lesson was that Iran’s nuclear ambitions cannot be eliminated simply through airstrikes. Tehran was likely to continue to move sensitive parts of its nuclear program underground, he added, making a lasting diplomatic settlement the only durable solution unless the US was prepared to contemplate a much broader military commitment.