US President Donald Trump has threatened to strike Iran's Pickaxe Mountain, home to a heavily fortified underground complex linked to Tehran's nuclear programme that has not been inspected by international monitors since construction began in late 2020.
Nuclear experts told The New Arab that while the site was a likely military target because of its strategic importance, conventional US bunker-buster bombs may be unable to destroy the deeply buried facility. They also warned that any strike could further undermine international oversight of Iran's nuclear programme while risking wider regional escalation.
"There is therefore a tension between maximalist promises to 'take out' the mountain and more uncertain efforts that conventional weapons can achieve," Benjamin Ashraf, an analyst at the Open Nuclear Network (ONN), told The New Arab.
What is Pickaxe Mountain?
Pickaxe Mountain, known in Iran as Kuh-e Kolang Gaz La, lies in the Zagros mountain range in Isfahan province, around two kilometres from the Natanz uranium enrichment complex.
Trump thrust the site into the spotlight on Monday during an interview with US radio host Hugh Hewitt.
Asked whether Iran possessed a fourth nuclear site after previous US attacks on Natanz, Isfahan and Fordow, Trump described the mountain as a potential target for "a good, big, beautiful strike right through the front door", adding that Americans "may see that very soon".
He also said he wanted the International Atomic Energy Agency (IAEA) to inspect the site, while claiming Washington had not yet detected activity there.
The threat comes despite Trump's repeated assertions that previous US attacks had severely damaged Iran's nuclear programme.
What do experts know about Pickaxe Mountain?
Ashraf said ONN's assessment was based entirely on satellite imagery and open-source analysis because the IAEA has had no access to the site since tunnelling began in late 2020.
The underground complex sits within the broader Natanz area but appears to be significantly deeper than Natanz's original buried centrifuge halls.
Satellite imagery and terrain analysis suggest Iran has excavated large underground galleries around 100 metres below the surface inside a granite ridge.
"Granite has a much higher compressive strength than the sedimentary limestone and dolostone above sites like Fordow, meaning the rock itself is better at absorbing and dispersing the shock from conventional bunker-buster bombs," Ashraf said.
Recent high-resolution imagery also appears to show construction continuing after the US-Iran memorandum of understanding committed both sides to maintaining the status quo at nuclear-related facilities.
Vehicles have been observed using western access roads, while tunnel entrances appear to have been reinforced with concrete headworks and additional protective overburden.
Other tunnel portals remain partially backfilled, limiting rapid vehicle access and suggesting Iran is controlling which parts of the complex remain active.
"Taken together, these features lead ONN to assess Pickaxe as a deeply buried, nuclear-related site being actively hardened and prepared for large-scale industrial use," Ashraf said.
What is believed to be inside the mountain?
Iran has said the underground complex is intended to house a centrifuge assembly facility following the destruction of an earlier plant in what Tehran described as an act of sabotage in 2020.
Iranian authorities have released few technical details, and no international inspectors have independently verified the site's purpose.
According to Maxar Technologies, tunnelling began in December 2020.
Independent imagery-based studies suggest the underground chambers are large enough to accommodate a modern centrifuge assembly plant. ONN says the site's size, depth and protection could also make it suitable for future uranium enrichment or other nuclear-related work should Tehran choose to expand its programme underground.
The Washington Post reported last year that construction intensified after previous US attacks, while the Institute for Science and International Security published satellite images showing heavy construction vehicles, drilling equipment, cranes and reinforced tunnel entrances.
Iranian parliamentary adviser Mehdi Mohammadi described the site this week as "the most heavily fortified nuclear facility in the world".
Could conventional US weapons destroy it?
Ashraf said the site's strategic value makes it an obvious military target, but warned there is a significant difference between damaging the complex and destroying it.
Research into deeply buried facilities suggests even the largest conventional bunker-buster bombs may disrupt such sites without reliably eliminating underground halls protected by strong rock.
"The United States can almost certainly crater portals, collapse access tunnels and sever power and ventilation at Pickaxe," Ashraf said.
"It is much harder to guarantee the elimination of all underground halls 80–100 metres down without either nuclear use or post-strike inspection, neither of which is being contemplated."
Without international inspectors being granted access afterwards, it would also be difficult to independently verify the extent of any damage underground.
What are the risks of attacking Pickaxe?
Ashraf warned that a partial strike could leave the core of the underground complex intact while making it even harder for international inspectors to monitor Iran's nuclear activities.
"Technically, a partial strike that leaves core halls intact could provide Iran with a damaged but repairable, harder-to-monitor underground capability," he said.
He added that bombing the site without restoring inspector access risked repeating the uncertainty that followed previous attacks on Natanz, Fordow and Isfahan.
"From a verification perspective, bombing without restoring inspector access risks repeating what we saw after the 2025 strikes on Natanz, Fordow and Esfahan: strong rhetoric about 'obliteration' alongside surviving enriched uranium, damaged but usable infrastructure, and continued construction at deeper sites."
Ashraf also noted that recent attacks near the Bushehr nuclear power plant had already raised concerns about military operations targeting or occurring close to nuclear-related infrastructure.
"We have already seen attacks near the Bushehr nuclear power plant, with strikes landing close enough to raise serious questions about how far combatants are prepared to go in hitting nuclear-adjacent infrastructure."
How has Iran responded?
Iran has not formally responded to Trump's latest threat.
However, Mehdi Mohammadi, an adviser to the speaker of Iran's parliament, described Pickaxe Mountain as "the most heavily fortified nuclear facility in the world".
He argued that Trump's consideration of attacking the site showed Washington had exhausted its military options and was moving towards an operation that was "doomed to failure from the outset".
Mohammadi said US Central Command's own documents showed the complex could not be successfully destroyed and described it as "untargetable".
"When the enemy reaches this level of operational desperation, it means it has reached the end of the road and entered this war without a plan," he said.
He warned that any attack on the facility "will turn the region into hell", adding that Iran "will turn the region upside down over the Americans, and this will certainly happen".
Mohammadi said Washington was seeking to force Iran to change its negotiating position on the Strait of Hormuz and its nuclear programme.
"They may try to damage Iran's nuclear materials to remove this issue from the negotiations, but they will certainly not succeed in this objective," he said.
He added that the coming period would bring "major developments in Iran's nuclear field, and unprecedented operations against the United States in the region".