Among the Iranian nuclear facilities the U.S. reportedly targeted in Sunday morning’s attack was the Pickaxe Mountain Facility. Iran has not acknowledged the site’s development or construction and it has retained a lower public profile, with the Institute for Science and International Security first discovering its existence in 2023. 

The facility, just south of the Natanz nuclear facility and buried roughly 330 feet below the mountain itself, was particularly concerning to experts due to its depth, which is between 30 to 70 feet deeper than Fordow. This is said to exceed the striking depth of the most powerful bunker-busting weapons in the U.S. arsenal.

Recent Iranian announcements stating the government planned to open a new facility heightened fears that Iran could take the site online in the near future, according to Andrea Stricker, the deputy director of the nonproliferation and biodefense program at the Foundation for Defense of Democracies.

“There’s concern that Iran was creating the floor space for another secret enrichment facility,” Stricker told Jewish Insider. “And so when the [International Atomic Energy Agency] Board of Governors passed a resolution finding Iran in non-compliance with the Nuclear Non-Proliferation Treaty a couple of weeks ago, the Iranians threatened to build another or to open another enrichment facility, and people immediately feared that this would be the site of it.”

An additional concern over the potential opening of Pickaxe Mountain was that Iran had previously refused to give notice of new nuclear facilities, as required by agreements Iran had signed with the IAEA. According to Stricker, this meant that Iran might begin operations at the plant without notifying the international community, which may have been a factor in Israel’s decision to launch its current operation against Iranian nuclear and military facilities.