Trump Points to Iran’s Resumption of Nuclear Activities at a New, Deeper Site

President Donald Trump’s remarks on Iran’s resumption of covert nuclear activities at an underground site highlight lingering concerns over the status of the Tehran regime’s nuclear program as Operation Epic Fury heads into its third week.  

Trump said Iran’s rulers had continued their pursuit of a nuclear weapon “even after we obliterated their key nuclear sites” in U.S. airstrikes last June. “They were starting work at another site, a different site … that was protected by granite … they wanted to go a lot deeper and they started the process,” he observed.

Coupled with the possibility that Tehran could recover highly enriched uranium (HEU) from previously struck nuclear facilities, these latest activities underscore the challenges ahead on the nuclear front for the combined U.S. and Israeli military campaign against the regime.

New Efforts Spotlight Pickaxe Mountain Facility

The “different site” Trump mentioned was likely the facility at Pickaxe Mountain, which is under construction near the Natanz nuclear complex and buried up to 100 meters below a mountain of granite. The United States and Israel did not target the site during strikes in June 2025, likely because it was not yet nearing completion. Since then, satellite imagery assessments by the Institute for Science and International Security have noted ongoing construction and fortification of entrances and security perimeters.

Iran officially claims it has been building a new centrifuge assembly plant at Pickaxe Mountain since 2021. However, Western intelligence assesses that Iran may intend to establish a new enrichment facility there — deeper than the underground enrichment facility at Fordow, which the United States damaged or destroyed last June, and potentially beyond the reach of aerial strikes. By going deeper, Iran likely hopes to limit the threat posed by the U.S. military’s Massive Ordnance Penetrator (MOP) bunker-busting bombs that can reportedly penetrate 60 meters below ground. These were deployed by the United States in its previous attack on Fordow.

Washington Weighing Options To Secure Tehran’s Highly Enriched Uranium Stocks

Iran’s ability to retrieve its HEU stocks — enough to produce up to 11 nuclear bombs — remains uncertain. The HEU is primarily dispersed between the destroyed Fordow enrichment plant, where Iran was enriching uranium to 60 percent, and the Esfahan tunnel complex, located close to where the United States and Israel struck uranium conversion, metal, and fuel production capabilities during last June’s campaign.

International Atomic Energy Agency (IAEA) Director-General Rafael Grossi confirmed on March 9 that roughly half of Iran’s HEU stockpile of 440 kilograms was stored in the Esfahan tunnels, where Tehran was also building a new enrichment plant. The IAEA last verified the stockpile shortly before Israeli strikes on Iran began on June 13, 2025. Nine days later, the United States destroyed the Esfahan tunnel entrances with Tomahawk missiles.

Trump told Fox News on March 10 that Iran has not yet moved the HEU from either Fordow or Esfahan. Media reports suggest Tehran may have created a narrow access point to reach the material but has not proceeded due to the risk of U.S. or Israeli strikes.

Trump is reportedly considering a special forces ground operation to breach the Esfahan tunnels and eliminate or seize the HEU stockpile, though he currently denies that such a decision is near.  

Iran’s Remaining Nuclear Threats Must Be Neutralized

Before the United States and Israel end major combat operations against Iran, they must complete two urgent tasks. First, they must neutralize Pickaxe Mountain. Second, they must recover or eliminate HEU stocks to prevent them from falling into the hands of surviving leaders of the Islamic Republic, other adversarial states, or Tehran’s terrorist proxies.

If special forces raids or longer-term HEU recovery efforts are more effective than utilizing MOPs, these should occur when the security situation permits and the military is confident it can limit casualties. The United States has long trained teams with expertise in disabling nuclear sites and disposing of nuclear materials safely.

In the meantime, the United States and Israel must continue closely monitoring these sites and preemptively strike anyone attempting to access them.

Andrea Stricker is a research fellow and deputy director of the Nonproliferation Program at the Foundation for Defense of Democracies (FDD). For more analysis from the author and FDD, please subscribe HERE. Follow Andrea on X @StrickerNonpro. Follow FDD on X @FDD. FDD is a Washington, DC-based, nonpartisan research institute focused on national security and foreign policy.