“ Iran says military sites are off-limits for nuclear inspections despite U.S. pressure”
https://www.latimes.com/world/asia/la-fg-iran-nuclear-201708...
American withdrew from the deal in May 2018 because Iran would not allow independent auditors to inspect all known or suspected sites.
See also this from 2015:
“The Iranian Nuclear-Inspection Charade Iran is allowed ample time, up to 24 days, to hide or destroy evidence before inspectors are given access.”
https://www.wsj.com/articles/the-iranian-nuclear-inspection-...
There were other instances going back to 2005.