‘Surge in construction’ at suspected Iranian nuclear site, analysts say, as US considers ways to strike deep underground

By Davis Winkie, Zachary Cohen, Thomas Bordeaux, CNN

(CNN) — A suspected Iranian nuclear site buried under granite has seen a flurry of construction work this year as the war with the US has transpired, according to a group of analysts who reviewed six years of satellite imagery.

The Pickaxe Mountain site, located near the Natanz nuclear complex roughly 140 miles south of Tehran, has been the subject of steady discussion by intelligence agencies which view it as a likely location for Iran to protect future nuclear program efforts.

According to a new satellite imagery analysis by the Center for Strategic and International Studies think tank, shared exclusively with CNN ahead of its publication, there has been “a clear surge in construction activity” this year.

The underground facility is “likely” designed to be a safe haven for Iran’s nuclear program, according to the CSIS analysts.

Israeli intelligence has suggested that Iran may be seeking to move centrifuges to the location as part of uranium enrichment efforts, and President Donald Trump has repeatedly threatened to strike the site.

“We may hit Pickaxe very soon,” Trump told reporters last week, adding that “we know everybody that’s moving” at the site.

The granite mountain, however, presents a difficult target to even the Pentagon’s “heaviest non-nuclear” bombs, the CSIS team reported. And It’s not the only Iranian nuclear facility feared to be out of reach for current-generation weapons.

But there are signs the US is working to devise some means of striking those sites, even as US forces have largely focused on other types of targets during the six-month conflict with Iran.

Four days before the US launched Operation Epic Fury, a program manager at an obscure Pentagon agency charged with combating weapons of mass destruction signed an emergency $1.2 million contract justification to repair a “unique subterranean test facility at White Sands Missile Range” in New Mexico for a “live-fire test designed to validate classified capabilities against rapidly emerging threats.”

The document from the Defense Threat Reduction Agency was uploaded to a federal database on February 27 — the day before the war started.

The memo said the “rapid test prep,” as another database labeled the contract awarded to Pate Construction, needed to be complete within two-to-three weeks due to “a time-sensitive national security directive.”

The plans for the test were connected to the Iran war, three sources familiar with the matter told CNN, and the need to develop a way to target Iran’s deepest-buried underground facilities and, likely, simulate US strikes against specific nuclear facilities.

The US previously struck nuclear sites in June 2025 as part of what the military called Operation Midnight Hammer. While the strikes successfully destroyed some key locations linked to Tehran’s nuclear program, a top US general told lawmakers last year that the deeply buried Isfahan nuclear site only had its entrances buried because the Pentagon believed its bunker-busting bombs — known as the Massive Ordnance Penetrator — could not knock it out.

The military is working to develop a “next generation penetrator” bomb to succeed the current MOP and potentially hit targets even more deeply buried. A contract to begin work on a prototype was awarded in September 2025, and the Air Force solicited defense industry sources for the new weapon in June.

Satellite imagery reviewed by CNN shows that between February 16 and February 18, excavation work began at a remote DTRA and US Strategic Command-operated site at White Sands intended to test the effects of weapons on deeply buried targets. The timing aligns with that of the emergency contract: Pate Construction provided an estimate for the test work on February 17 and received the deal the next day, according to federal contracting records.

Work at the remote location, known as the Alternate Seismic Hardrock in Situ Test Site, continued into mid-March as a pile of excavation dirt gradually grew. The round of activity appeared to halt then, according to the imagery.

Similar to Pickaxe Mountain, the DTRA test site in White Sands is also carved into granite, according to an environmental assessment.

CNN could not independently verify whether the test occurred, nor could CNN confirm the purpose of the work at the DTRA test site observed via satellite imagery. The Pentagon did not immediately reply to questions from CNN. Pate Construction did not return calls from a CNN reporter.

The US military maintains operational plans for strikes against Pickaxe, and it was part of a target package that was under consideration earlier this summer when Trump was threatening to escalate the conflict with Iran, according to a source familiar with the matter. The strike plan for Pickaxe involved using some of the largest bombs in the US arsenal, though it remains unclear if those munitions can penetrate deep enough underground to destroy whatever Iran may have moved there, the source added.

Efforts to develop plans for decisive strikes against underground facilities continue; a source familiar with the matter told CNN that elements within the Defense Department recently held a “planning sprint” on the topic.

The facility at Pickaxe Mountain is “likely” designed for one of three purposes, all related to Iran’s nuclear program, according to the CSIS analysis. It could be a centrifuge assembly facility, an enrichment facility, or a safe haven for other “nuclear weapons-relevant” work such as uranium metal conversion.

In their report, the CSIS analysts argued the construction at the site “has shifted from active excavation toward probably internal construction and continued exterior reinforcement.” Pickaxe Mountain in 2026 has seen “more road activity” than ever before, and additional work has included “raising and hardening of the (tunnel) portal accesses, paving of the internal road network, reinforcement around access areas, and the flattening and removal” of dirt excavated while building its tunnels, the report said.

The CSIS analysts cautioned that the “continuous construction” they’ve observed at Pickaxe Mountain, among other factors, suggests the site “is not yet capable of enrichment work, if that is the intended purpose.”

CNN’s Tal Shalev contributed to this report.

Davis Winkie’s work at CNN is supported by a partnership between Outrider Foundation and Journalism Funding Partners (JFP). CNN retains full editorial control of the reporting.

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