In recent weeks, Iran has intensified its efforts to isolate its stockpile of enriched uranium close to the level needed to manufacture a nuclear bomb, deliberately collapsing tunnels and placing explosive mines at entrances, according to five sources familiar with the information from American intelligence services.
Access to approximately half a ton of highly enriched uranium is now much more difficult, dangerous, and time-consuming than it was just a month ago, when President Donald Trump publicly signaled that he might order the US military to confiscate it, sources told CNN.
The new fortifications built by the Iranians add an additional level of complexity to the proposed agreement by the Trump administration with Tehran for the removal and destruction of uranium, and this measure raises questions about who will take on the dangerous task of recovering it.
The Iranian diplomatic delegation to the United Nations did not immediately respond to a request for comments, and the White House did not immediately respond to questions from CNN.
Trump has repeatedly stated that securing this material is a priority for the United States in the ongoing negotiations to end the war and reopen the Strait of Hormuz, which Iran effectively closed.
According to a senior administration official, the two parties are gradually approaching an agreement that would require Iran to hand over its enriched uranium to the United States. According to the official, it would then be destroyed on-site and then removed from the country.
However, American and Iranian officials have presented conflicting versions of the provisional agreement, and the exact terms of it remain unclear. The alleged text of a draft agreement was disclosed to a semi-official Iranian news agency on Friday, prompting a furious reaction from Trump on social media.
Several sources have stated that, even for the Iranians, removing the enriched material would now be difficult and dangerous. It would require heavy excavation equipment and demining operations, both of which are complex and risky.
"If this information is true, it would certainly complicate the recovery of highly enriched uranium (HEU)," said Scott Roecker, who led the Office for Nuclear Material Removal at the National Nuclear Security Administration between 2017 and 2021.
The situation could also provide Iran with an opportunity to hide or distort its compliance efforts.
"If negotiators 'will request Iran to bring the entire stock to a central location for verification and, ultimately, for the removal or dilution of the material,' the responsibility for accessing and providing the 'full inventory' of enriched uranium would fall to Tehran," Roecker explained.
However, "in this scenario, I would fear that Iran could claim that some of the highly enriched uranium is impossible to recover," he added. "I would not have full confidence that Iran could not regain access to that material in the future."
The international community believes that most of the stockpile is in collapsed tunnels within the Isfahan nuclear complex, located in central Iran, with an additional quantity stored in other locations.
In mid-May, the US military was prepared to carry out an operation to confiscate the nuclear material, but this was ultimately deemed too risky, as previously reported by CNN.
Meanwhile, Iran has further fortified the locations where its highly enriched uranium is believed to be buried underground.
Trump previously acknowledged the dangers of forcibly retrieving the uranium and expressed skepticism, in a May appearance on Fox News, that the Iranians could ever access and recover the buried nuclear material without US intelligence services detecting the operation.
"We know exactly what's going on," Trump told moderator Sean Hannity about the location. "No one has even come close to it."
However, as two sources noted, publicly discussing uranium as a possible target, the president may have provided Iran with the motivation to better defend its own assets.
Now, even if the agreement between Tehran and Washington is signed next week, additional technical negotiations are expected to establish the details of Iran's future nuclear program.
Removing the uranium from the country would likely require the deployment of a specialized mobile facility for uranium processing, organized under the authority of the National Nuclear Security Administration at the Oak Ridge National Laboratory in Tennessee. CNN previously reported that top American negotiators, Jared Kushner and Steve Witkoff, visited the laboratory earlier this month.
However, even the world's best experts in nuclear material removal would need considerable time to accomplish their mission. Trump told reporters earlier this month that the removal operation would take at least two weeks.