The US and Israel struck key nuclear facilities during last June’s 12-day war. Uncertainty over Iran’s highly enriched uranium has intensified because it’s almost nine months since United Nations atomic inspectors last verified its location, the officials said. They spoke on condition of anonymity to discuss restricted deliberations.

“They haven’t been able to get to it and at some point, maybe we will,” Trump said late on Saturday during a briefing aboard Air Force One. “We haven’t gone after it, but it’s something we can do later on. We wouldn’t do it now.”

One of the stated aims of the attacks on Iran has been to rid the Islamic Republic of any capability to produce nuclear weapons. But the strikes on atomic facilities last year complicated the task of tracking the uranium. That’s now become a live issue again for military planners, and it’s unclear whether any special operation would be conducted by US or Israeli forces.

Publicly, US officials have projected confidence that they know where the uranium is stored. Privately, there is said to be less certainty. In the weeks before the latest US and Israeli strikes, monitors from the Vienna-based International Atomic Energy Agency observed sustained activity outside tunnels built into a hillside near Isfahan, where the material was last documented before the fighting began.

That activity increases the likelihood that at least some of the 441 kilograms (972 pounds) of highly enriched uranium stored at the complex was moved, said a diplomat in the Austrian capital familiar with the agency’s assessments. 

The stockpile is sufficient for roughly a dozen nuclear warheads if further refined, with the US saying specifically 11 bombs. Iran also possesses more than 8,000 kilograms of uranium enriched to lower levels, material that could be upgraded if enrichment capacity is restored.

US and Israeli officials are actively searching for the highly enriched material and have contingency plans that include deploying special forces if its location is confirmed, one of the officials said.

A senior Trump administration official said on March 3 that the US had two options to render Iran’s enriched uranium unusable. If the US had physical control of the territory, people could be sent in to dilute it on-site and safely dispense of it, the official said. They could otherwise remove it from Iran and deal with it in another location, the official said.

Axios reported earlier that the US and Israel were looking at potential ground forces to seize Iran’s nuclear stockpile. The White House didn’t respond to requests for comment on any potential plan. 

Trump said on Saturday he didn’t want to talk about ground troops, though he didn’t rule out the possibility. He said they would have to be “for a very good reason” and if they were ever used, Iran would have to be so “decimated that they wouldn’t be able to fight at the ground level.”

The US military has prepared detailed plans for incursions into Iran in the past. One such operation, named Project Honey Badger and developed decades ago in the wake of the US embassy hostage crisis, envisioned airlifting roughly 2,400 special operations troops on more than 100 aircraft into Iran.

The plan involved transporting excavation equipment, including a heavy bulldozer, that would be critical for troops if they needed to remove buried uranium. 

First, though, the US and Israel would have to find it. Before the June conflict, Iran was the world’s most heavily inspected nuclear program, with IAEA monitors averaging more than one visit per day to declared facilities. That access ended after strikes hit Iran’s main enrichment plants at Fordow and Natanz, as well as its uranium processing center in Isfahan.

Even before the latest attack, Tehran’s government flagged it was prepared to take special measures to preserve the material. “The agency should not expect safeguard measures to be implemented under such wartime conditions as if hostilities had not occurred,” said Reza Najafi, Iran’s envoy to the IAEA.

Tehran had previously signaled it was open to reducing or exporting its highly enriched stockpile as part of a broader diplomatic agreement. The latest round of fighting halted those negotiations.

The collapse of diplomacy has forced the US and Israel to review military contingencies, including the possibility of using ground forces to retrieve nuclear material, said a European official familiar with the planning.

One key challenge they would face is that it could be dispersed and then concealed indefinitely.

According to US regulatory estimates, the highly enriched uranium could be stored in roughly 16 cylinders about 36 inches (91 centimeters) tall, comparable in size to large scuba tanks. Each cylinder would weigh about 25 kilograms, light enough to be transported by vehicle or even potentially by hand.

It remains uncertain how much damage the US and Israel have inflicted on Iran’s enrichment infrastructure. Even if it’s significant, the existence of uranium close to weapons grade outside monitored facilities poses a continuing risk.

Most analysts, including inside US intelligence, agree Iran hasn’t decided to pursue weapons and the IAEA hasn’t detected a structured weapons program. The probability Iran decides to build a nuclear weapon remains below 50%, according to the Institute for Science and International Security.

But the death of Supreme Leader Ayatollah Ali Khamenei in the opening hours of the war has triggered a succession process that could reshape nuclear decision-making. Khamenei had issued a religious edict, or fatwa, against developing nuclear weapons. A successor could revisit that stance.

Iran, joined last week by China and Russia, has indicated that “a sustainable diplomatic solution” remains possible, according to remarks at the IAEA. But recent statements from Trump suggest the administration is prepared to pursue its objectives militarily.