US President Donald Trump has repeatedly threatened to bomb an under-construction Iranian nuclear facility buried deep beneath a mountain, as the United States and Iran continue exchanging strikes over the Strait of Hormuz.
The site, known as Kuh-e Kolang Gaz La, or "Pickaxe Mountain," is located south of Iran's Natanz uranium enrichment complex, which was bombed by the United States during Operation Midnight Hammer in the 12-day Iran-Israel war in 2025. However, Pickaxe Mountain remained untouched, with Iran continuing excavation work at the site.
It remains unclear what exactly is being built inside Pickaxe Mountain, as the International Atomic Energy Agency (IAEA), the UN's nuclear watchdog, has never been granted access to the facility. Speaking to reporters in the Oval Office on July 21, Trump acknowledged the possibility that Iran may have moved uranium-enrichment centrifuges to the underground complex, potentially at a depth beyond the reach of even America's most powerful bunker-buster bombs.
"We'll be hitting that area… probably pretty soon. And there's not a thing they can do about it," Trump said.
Here's what we know about Pickaxe Mountain and the current status of Iran's nuclear programme.
The Pickaxe Mountain project is being developed adjacent to the Natanz nuclear complex, around 225 kilometres south of Tehran.
Natanz, which includes both above-ground and underground facilities, has been under international scrutiny since its existence became public more than two decades ago. A series of sabotage attacks—including one widely attributed to Israel that destroyed a centrifuge manufacturing facility—prompted Iran to begin construction of the underground complex at Pickaxe Mountain.
Protected by anti-aircraft batteries, perimeter fencing and Iran's Islamic Revolutionary Guard Corps (IRGC), the site spans nearly 2.7 square kilometres across Iran's central plateau. Satellite imagery shows multiple tunnel entrances.
An Associated Press investigation published in 2023, citing experts from the James Martin Center for Nonproliferation Studies, estimated that the facility was being built 80 to 100 metres underground. Continued excavation since then has led some analysts to believe it may now extend even deeper.
Experts believe the scale of construction suggests Iran intends to use the facility both to enrich uranium and manufacture centrifuges.
Centrifuges are cylindrical machines that rapidly spin uranium gas to increase its concentration of the fissile isotope needed for nuclear fuel—and potentially nuclear weapons. Housing large centrifuge cascades underground would provide Iran with greater protection from aerial attacks while enabling faster uranium enrichment.
The United States developed the GBU-57 Massive Ordnance Penetrator specifically to destroy deeply buried targets. According to the US military, the bomb can penetrate at least 60 metres of earth before detonating. US defence officials have reportedly considered using multiple GBU-57 bombs in succession to maximise penetration, although experts remain uncertain whether even that would destroy a facility as deep as Pickaxe Mountain.
Speaking alongside Lebanese President Joseph Aoun on Tuesday, Trump initially downplayed the importance of Pickaxe Mountain by focusing on Iran's stockpile of highly enriched uranium.
Before the 2025 conflict, Iran had enriched uranium to 60 per cent purity—just below weapons-grade levels. Since the US strikes, there has been no confirmed evidence that Tehran has resumed uranium enrichment, and most of its enriched uranium is believed to remain at the bombed nuclear facilities.
"We follow the material, that's where the action is," Trump told reporters.
However, he later identified Pickaxe Mountain as a potential military target as hostilities between Washington and Tehran continued.
"Normally I wouldn't say that," Trump said. "If I thought they could do something about it, I would never say that, but we'll be hitting that area pretty soon. And very heavily."
Iran has claimed that areas surrounding its only operational nuclear power plant at Bushehr have come under attack during the conflict, although officials said the Russian-operated reactor was not damaged.
Tehran also alleged that the United States struck the cleared site designated for the planned Darkhovin nuclear power plant. However, the IAEA said there was no nuclear material at the location during its most recent inspection.
The Barakah Nuclear Power Plant in the United Arab Emirates—the country's only nuclear power facility—has also reportedly been targeted during the conflict.
Iran has warned that it will take unspecified "required actions" in response to the alleged attack on the Darkhovin site.
In 2025, the United States bombed Iran's nuclear facilities at Fordo, Isfahan and Natanz, all of which were involved in uranium enrichment.
Both Washington and Israel have repeatedly said their objective is to prevent Iran from acquiring a nuclear weapon.
Iran has consistently maintained that its nuclear programme is intended solely for peaceful purposes. The IAEA and Western intelligence agencies have long assessed that Tehran has not operated an active military nuclear weapons programme since 2003.
However, Iranian officials have increasingly suggested that the country could pursue nuclear weapons if faced with growing external threats.
Former Supreme Leader Ayatollah Ali Khamenei, who was killed on February 28, 2025, during the opening phase of the conflict, had issued a religious ruling (fatwa) declaring nuclear weapons to be un-Islamic. His successor, Mojtaba Khamenei, has not publicly clarified his position on the issue.
To build a functional nuclear weapon, Iran would first need to enrich uranium to approximately 90 per cent purity, then develop and assemble a workable nuclear device, miniaturise it, and integrate it with a ballistic missile. Experts say that process would likely take several months or even years and would carry a high risk of detection by US or Israeli intelligence agencies.