JD Vance has suggested Iran’s estimated 400kg (882lb) stockpile of enriched uranium, which is just short of weapons-grade, remains intact despite the recent US bombing campaign against Iran.

On Monday, the vice-president told Fox News that the location of the uranium “is not the question before us”, and said the relevant question was: “Can Iran enrich the uranium to weapons-grade level and can they convert that fuel into a nuclear weapon?”

The Iranian stockpile of uranium was believed to have been located mainly at Isfahan, which houses a conversion facility that turns uranium into the form that can be fed into centrifuges for enrichment.

However, the UN atomic energy agency chief, Rafael Grossi, said in recent days that the stockpile could have been moved. His inspectors have not been able to visit Iranian nuclear sites since the war began.

The US bombed nuclear facilities at Fordow, Natanz and Isfahan on Saturday in an attempt to destroy Iran’s nuclear program, but reports suggest that despite massive physical damage to the sites, the uranium itself was probably moved elsewhere.

“The goal was to bury the uranium, and I do think the uranium is buried,” Vance said. Of the US, he said the goal of the bombing “was to eliminate the enrichment and eliminate their ability to convert that enriched fuel into a nuclear weapon. We don’t want that 60%-enriched uranium to become 90% enriched uranium. That’s the real concern”.

But Vance insisted it was not a concern that Iran could have moved it and claimed the bombing represented “mission success” because he said Iran no longer had the capacity to turn the stockpile into weapons-grade uranium. “And that was really the goal here,” he said.

The former UN nuclear weapons inspector David Albright told CNN on Monday there are centrifuges that are “unaccounted for” that must still be dealt with to consider the US mission successful.

“I think that part of the mission has been accomplished,” he said. “Stocks of enriched uranium are one of them. I wish those stocks were buried, but our understanding is that some of them were taken away by Iran, and we don’t know where they are.”

Albright added that the question of the remaining, unaccounted-for centrifuges meant that “this problem isn’t over yet, but it is a manageable problem. Partly because turning that enriched uranium into weapons-grade uranium is not going to be a slow – a fast process”.

Asked if that enriched uranium stockpile had been destroyed, Vance told ABC’s This Week program on Sunday that “we are going to work in the coming weeks to ensure that we do something with that fuel and that’s one of the things that we’re going to have conversations with the Iranians about”.

Iran has made clear it does not wish to discuss the stockpile, and it may represent one of the remaining cards it has left to play. Grossi told the New York Times that the fuel was last seen by his teams of inspectors from the International Atomic Energy Agency about a week before Israel first attacked on Iran.

In an interview on Sunday, Grossi said: “Iran has made no secret that they have protected this material.”