What is Iran's Pickaxe Mountain and why does Trump say he wants to bomb it?
Shayan Sardarizadeh, Jake Horton and Ghoncheh HabibiazadBBC Verify and BBC Persian
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US President Donald Trump has repeatedly threatened to bomb a suspected underground nuclear site in Iran known as Pickaxe Mountain, where recent satellite images appear to show construction work taking place.
Pickaxe Mountain is one of the few Iranian sites linked to the country's nuclear programme that has not been the target of US and Israeli strikes. There have been unproven claims that some of Iran's stock of highly enriched uranium may be kept there, which could be further enriched for use in nuclear weapons.
"We'll be hitting that area pretty soon, and very heavily," Trump told reporters on 21 July. And on 28 July he said: "I know exactly what's going on at Pickaxe. It's not a big problem - we took out their nuclear sites, and we'll have to take out Pickaxe if we don't make a deal."
Iran's foreign ministry spokesperson Esmail Baghaei said on 22 July that "no nuclear activity is taking place" at Pickaxe Mountain, and described US threats as "a fabricated pretext for aggression, destruction, and sabotage".
BBC Verify and BBC Persian have spoken to experts and analysed satellite imagery to piece together what we know about the site, and the potential impact of any strike.
What do we know about Pickaxe Mountain?
Kuh-e Kolang, which translates as Pickaxe Mountain, is located immediately south of the Natanz nuclear complex, Iran's largest uranium enrichment facility which has been bombed by both the US and Israel in 2025 and 2026.
The site is believed to be buried deep inside the mountain and its exact purpose is shrouded in mystery and speculation.
Tehran has previously indicated that it may be a replacement for a building within the Natanz complex used for the assembly of advanced centrifuges that was damaged after a suspected sabotage operation in July 2020.
Former head of the Atomic Energy Organisation of Iran, Ali Akbar Salehi, said in September 2020 that "a more modern, spacious, and comprehensive facility" would be built in the mountains "near Natanz", without naming Pickaxe Mountain.
Centrifuges are needed to produce enriched uranium, which can be used to make reactor fuel for civilian use but also for nuclear weapons if enriched to around 90% purity or higher.
The facility appears to have four tunnel entrances, two on the eastern side and two on the western end. Satellite images show that - over time - what appears to be a large perimeter fence has been built around the site, following the 12-day war between Israel and Iran in June 2025.
Images captured on 30 June 2026 show several construction vehicles near one of the western entrances. And in recent months, satellite imagery indicate continued work on access roads and tunnel entrances around Pickaxe Mountain.
According to analysis by the US-based Institute for Science and International Security (ISIS), Iran has partially filled the two eastern tunnels to block ground access.
"In the last year, we have observed fairly steady construction activity at the site," says Spencer Faragasso of the ISIS. "Iran's work there has likely centred around continued internal excavation and hardening of the facility that would provide further protection against aerial attacks."
Could US bombing destroy Pickaxe Mountain?
The site at Pickaxe Mountain may have been chosen to protect it from air strikes with some analysts estimating the core of the facility could be roughly 100m (328ft) underground.
This would also mean it's buried deeper than Iran's two nuclear enrichment complexes at Fordo and Natanz which the US bombed last year using what are known as bunker buster bombs - the only known weapon that could conceivably reach such concealed sites.
The US GBU-57 bomb weighs about 13,000kg (30,000lb) and is reported to able to penetrate 18m (60ft) of concrete or 61m (200ft) of earth before exploding.
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But even using these munitions, experts say the US would be unlikely to completely destroy Pickaxe Mountain.
"Obliterating every underground chamber would be extremely difficult because of the facility's depth and uncertain layout," says Arman Mahmoudian, a research fellow specialising in Iran at the University of South Florida.
However, the US could target tunnel entrances, communications systems, access roads, and other supporting infrastructure, Mahmoudian adds, which "could paralyse the facility's operations even if some of its deepest underground sections survived".
Meanwhile, Faragasso says the site may be potentially vulnerable and that "targeting the ventilation shafts would enable the weapons to reach deeper into the facility, and the tunnel portals can be collapsed using bunker buster weapons".
What do we know about what's underground at Pickaxe Mountain?
Information about exactly what is underground is not publicly known, and it is unclear whether the facility is operational.
The International Atomic Energy Agency (IAEA) - the global nuclear watchdog - has so far not been given access to Pickaxe Mountain by Tehran. Rafael Grossi, the director-general of the IAEA, said in March that Iran had "announced their intention to have nuclear activity there".
"This was part of their quite systematic intention to put their most sensitive facilities underground," Grossi added.
The IAEA estimated in 2025 that Iran holds roughly 440kg (970lbs) of 60% enriched uranium,
There have been unproven claims that part or all this stockpile may be kept at Pickaxe Mountain, or that some of the undamaged centrifuges at Natanz or Fordo may have been transferred there after the bombings of both facilities.
"It is plausible that high value items, such as uranium gas centrifuges, were brought into and stored within the tunnels," says Faragasso. "We have seen lots of continuous and steady truck movement throughout the site, entering and exiting the tunnel portals, meaning it is possible that some of those vehicles had moved items inside."
David Albright, the founder and President of the ISIS, says that the "concern is Pickaxe Mountain could be a location where Iran puts an enrichment plant that could produce weapon-grade uranium for nuclear weapons".
"None of this is happening as far as we know, but the fear is that it could turn into a place to make weapon grade uranium metal," Albright adds.
Tehran says its nuclear programme is for peaceful civilian use and denies any intention to develop nuclear weapons.
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