• President Donald Trump threatened to strike Iran’s Pickaxe Mountain underground complex, telling conservative broadcaster Hugh Hewitt that “Pickaxe Mountain is a possible target for a nice big fat shot.”
  • The subterranean facility under a 5,200-foot mountain ridge near the damaged Natanz enrichment site has not been inspected by the International Atomic Energy Agency, and experts assess it could house centrifuge enrichment plants capable of producing weapon-grade uranium.
  • U.S. and Israeli air attacks in 2025 and 2026 did not target Pickaxe, and the depth of its tunnels — 100 and 145 meters below the peak — may exceed the reach of America’s 30,000-pound bunker-buster bombs.
  • Iran has declined to provide design information to international monitors, and construction activity at the site resumed after the June 2025 strikes, according to satellite imagery analyzed by the Institute for Science and International Security.

Underground complex built after Natanz sabotage, experts say

President Trump has threatened to bomb Pickaxe Mountain, an Iranian underground complex under construction near the Natanz uranium enrichment facility, as the administration considers expanding military operations against Iran’s nuclear infrastructure.

In an interview with conservative broadcaster Hugh Hewitt, Trump said: “We have eyes on it and Pickaxe Mountain is a possible target for a nice big fat shot. Tell the Iranians to be ready.”

Iran said it began building the site in 2020, after an aboveground enrichment plant at Natanz was badly damaged in a suspected act of sabotage. The following year, the head of Iran’s nuclear agency said the facility would be used to house “sensitive” equipment.

Construction at the site appears incomplete, and it remains unclear whether any nuclear or other activity is taking place there. During Israeli and U.S. air attacks on Iran in 2025 and 2026, Pickaxe Mountain was not considered important enough to warrant strikes, according to the Wall Street Journal.

The subterranean complex sits under a mountain ridge more than 5,200 feet above sea level. The Institute for Science and International Security, a Washington-based think tank, estimated in 2022 that the facility could contain a workspace exceeding 5,000 square meters, or more than 53,000 square feet. One tunnel is 100 meters below the peak, another 145 meters, indicating multiple levels. Both tunnels have hardened entrances, the group said.

“The space available under the mountain could be expected to be large enough to also hold a centrifuge enrichment plant capable of producing weapon-grade uranium,” the institute said in its assessment. “It is likely large enough to also hold certain nuclear weaponization activities such as making weapon-grade uranium metal and shaping it into nuclear weapon components.”

Iran denies it has ever planned to build nuclear weapons, saying its program was for civilian purposes. U.S. officials have said Tehran is not currently believed to be enriching uranium.

The site has been under surveillance by the U.S. and Israel for years, but there are significant gaps in knowledge about it. Iran has declined to provide design information to the International Atomic Energy Agency. IAEA Director General Rafael Grossi said in March that inspectors should visit the site.

The depth of the tunnels may render them invulnerable to direct hits from the Massive Ordnance Penetrator bombs — 30,000-pound bunker busters — that the U.S. dropped on Natanz and Fordow. Iranian officials have said the site is designed to reduce vulnerability to such attacks. Publicly available satellite imagery has not revealed the locations of ventilation shafts at Pickaxe, which were known at Fordow from internal designs and surveillance.

“You can’t expect the same level of success from airstrikes at Pickaxe that we saw at Fordow,” said Matthew Sharp, senior nuclear fellow at the Massachusetts Institute of Technology and a former senior diplomat at the U.S. mission to the IAEA. The complex is deeper, he said, and “Fordow was really well understood in terms of its layout and vulnerabilities in a way that the new facility at Pickaxe just isn’t.”

Dan Shapiro, who served as a senior Pentagon official during the final year of the Biden administration, said Trump is concerned that “the setbacks the 12-day war imposed on Iran’s nuclear program could be reversed.” It could take time for Iran to begin enriching uranium at Pickaxe, he said, “but it does make the mountain a plausible target for attack.”

Experts note that the site has vulnerabilities despite its depth. Ongoing construction depends on power supplies, equipment deliveries, cooling and personnel — all of which could be targeted. Tunnel entrances could also be struck to set back Iranian work and make it clear when activities resumed.

The threat comes as the U.S. continues intermittent airstrikes in Iran. Trump said after the 2025 strikes that Iran’s nuclear program had been “obliterated,” but the U.S. bombed the sites again in 2026 in an effort to further bury fissile material thought to be held there.

Under a recent interim deal, Tehran pledged to dilute at least 441 kilograms of near weapons-grade fissile material — enough for 11 nuclear weapons — that it produced before the June 2025 conflict. That material is believed to be buried underground at Isfahan, Fordow and Natanz.