The good news might be that it will unlikely happen due to attribution. Experts would likely attempt to trace the origin of a nuclear uranium weapon through a variety of forensic techniques, including examining the radioactive isotope signatures left behind, via “nuclear forensics.” By analyzing the isotopic ratios and other chemical signatures, experts can potentially identify the source of the uranium used in the weapon much like in the film SUM OF ALL FEARS. However, the effectiveness of such tracing would depend on several factors, including the quality of the sample collected, the sophistication of the analytical techniques, and the availability of a comprehensive database against which to compare the findings.... requiring cooperation from multiple international agencies, so there are no guarantees of successful attribution. What do we know about any signatures from Iran?
The source of the uranium/plutonium is not the same as the source of the bomb, or the deliverer.