US President Trump threatens to bomb Iran's suspected underground nuclear site

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.

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, external 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.

The site at Pickaxe Mountain may have been chosen to protect it from air strikes with some analysts estimating, external 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.

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".