Iran's stance directly clashes with U.S. President Donald Trump 's position that Iran must halt all enrichment amid negotiations marked by uncertainty, despite having reached their most significant step since they began in April with a U.S. offer being delivered to Tehran last week.

U.N. inspectors monitoring Iran's Fordow nuclear site confronted a major gap in their knowledge last year as they watched trucks carrying advanced uranium-enriching centrifuges roll into the facility dug into a mountain south of Tehran.

President Trump claimed Monday that the U.S. won't allow Iran to enrich uranium under a potential nuclear deal. Why it matters: Trump's claim contradicts the proposal his envoy Steve Witkoff made to Iran on Saturday,