Days after the United States hit three of Iran’s main nuclear sites, uncertainty surrounds the 400 kg of 60 percent enriched uranium that had been stored at declared facilities but is now unaccounted for.

Though US officials quickly claimed to have degraded Iran’s nuclear capacity, both international monitors and regional analysts suspect that the most sensitive material may have been relocated ahead of the June 22 air strikes. 

If confirmed, the move raises new questions about the effectiveness of the operation and the assumptions underpinning it.

Signs of a preemptive move

Satellite imagery taken in the days before the strikes reveals unusual activity near the Fordow enrichment facility, an underground site long viewed as one of Iran’s most fortified nuclear installations. 

According to commercial imagery firm Maxar, photos from Thursday showed 16 cargo trucks lined up along the road leading to the Fordow tunnel entrance, with most repositioned a kilometre away by the next day. 

By Friday, two days before the American strikes, new trucks and multiple bulldozers had arrived near the tunnel itself – one truck parked right next to the entrance.

The exact nature of the activity remains unconfirmed. 

However, the Islamic Republic of Iran Broadcasting (IRIB), Iran's official radio and television broadcaster, reported on Sunday that targeted sites had been evacuated before the attack and sensitive nuclear materials were moved to safe locations, without providing details.

The three targeted facilities — Fordow, Natanz, and Isfahan — were all struck using a combination of bunker-buster bombs and cruise missiles. 

US claims and contradictions

US Vice President JD Vance stated on Sunday that although the US strikes were intended to destroy Iran’s nuclear infrastructure, he stopped short of confirming full destruction, saying instead the nuclear programme was “substantially set back”. 

He also indicated that Iran was now “much further away from the nuclear programme today than they were 24 hours ago”.

International Atomic Energy Agency (IAEA) Director General Rafael Grossi confirmed that his team last saw the stockpile between June 10 and 13 – days before the US strikes. 

Since then, access to Iranian facilities has been blocked, and the agency has formally asked Tehran to disclose the uranium’s current location.

At a meeting in Vienna, Grossi urged Iran to cooperate with inspections and allow the IAEA to verify that the material remains under safeguards. 

But some world leaders, including Russian Foreign Minister Sergey Lavrov, have criticised the agency’s approach.

“We searched and searched, but found nothing,” Lavrov said, describing the IAEA’s stance as assuming that Iran is hiding something simply because it hasn’t been found. 

“Now they’re demanding, ‘Show us where it is,’ without any guarantee that such sensitive information won’t leak.”

How Tehran could have moved it

Moving 400 kg of uranium enriched to 60 percent is a formidable task but not impossible. The material is typically stored in heavy steel cylinders and can be transported overland under strict security protocols. 

Experts say Iran’s decades-long experience in circumventing surveillance, alongside its extensive network of underground tunnels and fortified bunkers, makes such a transfer plausible.

Some believe the convoy seen near Fordow may have been part of this relocation effort. Others point to the possibility of smaller, more frequent shipments being moved in pieces. 

What remains uncertain is whether the uranium is now sitting in another hardened facility, buried underground, or even divided and hidden across multiple sites. Without access, the IAEA cannot verify any of these scenarios.

A victory in question

Though Washington framed the strikes as a decisive blow, the disappearance of Iran’s most sensitive nuclear material casts doubt on the narrative of a successful mission. 

Infrastructure may have been damaged, but Tehran’s enrichment capacity is ultimately tied to its ability to preserve its fuel and centrifuge technology.

A senior adviser to Iran’s Supreme Leader Ali Khamenei confirmed on Sunday that Iran’s stockpile of enriched uranium is still intact despite US attacks on three nuclear sites.

“Even if nuclear sites are destroyed, game isn’t over, enriched materials, indigenous knowledge, political will remain,” Ali Shamkhani wrote on X.

By withholding access and declining to disclose the material’s whereabouts, Tehran is signalling its intent to retain control over its programme regardless of military pressure.

Whether hidden underground or simply out of reach, Iran’s most enriched uranium is missing from declared sites, and no one knows exactly where it is.