The assessment came as experts are trying to determine how long it would take Iran to rebuild its nuclear program in the aftermath of U.S. and Israeli strikes.

Initially US President Donald Trump claimed the operation was a total success, but officials on both sides of the Atlantic are now acknowledging that significant quantities of enriched uranium may have withstood the bombardment.

Israel believes that Iran could potentially retrieve enriched uranium buried beneath one of the three facilities struck by US forces last month, according to a senior Israeli official.