S enior Israeli officials are acknowledging that some enriched uranium may have survived the powerful U.S. strikes on Iran's key nuclear sites last month.

The process of uranium enrichment increases the concentration of U-235, an isotope that can sustain a nuclear chain reaction. Beginning in 2006, the U.N. Security Council called on Iran to suspend all uranium enrichment, but it endorsed the JCPOA on July 20, 2015.

A senior Israeli official says Israel believes deeply buried stocks of enriched uranium at one Iranian nuclear facility hit by the U.S. military are potentially retrievable.