The Pentagon is contemplating what could become “the most sophisticated operation in military history”  to seize Iran’s stockpile of enriched uranium, the New York Post reported on Saturday, citing sources.

A source familiar with the matter told the outlet that the plan would send thousands of ground troops to storm heavily fortified nuclear sites, with a small team of elite commandos tasked with the actual retrieval.

The exact whereabouts of Iran’s enriched uranium – which could be key to creating nuclear weapons – are unclear. Tehran has four major nuclear facilities at Fordo, Natanz, Isfahan, and Pickaxe Mountain, with the former three coming under US-Israeli strikes last year. Out of an estimated 440kg of enriched uranium, roughly 200 kilograms are believed to be stored in deep tunnels outside Isfahan, with additional quantities thought to be at Natanz.

Iranian Foreign Minister Abbas Araghchi said in March that Tehran’s stockpile of highly enriched uranium remains buried “under the rubble” of the facilities hit by US and Israeli strikes, adding that Iran currently has “no plan” to recover or dilute it.

As for Pickaxe Mountain, a heavily fortified complex carved deep in the granite bedrock, it was spared in last year’s strikes because it was still under construction and largely empty at the time.

However, the facility has since been reportedly reinforced, with the US and Israel suggesting that Iran may have moved centrifuges – and potentially uranium – deeper underground there, though the site is not believed to be fully operational yet.

According to the NYP, regular US troops would be tasked with storming the facilities and forming a defense perimeter. In the meantime, much smaller forces, including Seal Team 6’s Silver Squadron, the Army’s 2nd Ranger Battalion, and the 21st Ordnance Company, would be handling and transporting the material once it is pulled from the mostly destroyed Fordo plant and the badly damaged Isfahan site, the report said.

The operation would reportedly require ground crews to clear booby traps and reopen collapsed tunnel entrances, with US warplanes tasked with establishing total control of an air corridor to fly out the uranium.

“I hate to say it, but I think the most likely way to get rid of Iran’s nuclear material, at least what they currently have, is a military operation because the negotiations aren’t going anywhere fast”, Joseph Rodgers, deputy director of the Center for Strategic and International Studies, told the NYP. He called the prospective raid potentially “the most sophisticated operation in military history,” pointing to the logistics of operating deep inside hostile territory while guarding multiple sensitive sites.

“This would be a logistically heavy and difficult operation in a contested environment,” Rodgers added. “Iran’s military is pretty destroyed, but they’re still more sophisticated than the Cubans that were guarding [Venezuelan leader Nicolas] Maduro.”

The New York Times reported last month that much of Iran’s uranium is believed buried so deep that even America’s most powerful bunker-buster bombs may fail to destroy it, warning that a retrieval raid would carry major risks as uranium can turn highly toxic if exposed to moisture.