Nobody asked for that. They asked for inspection of sites that show radionuclides emissions or specific heat signatures indicative of enrichment. I believe these are detected from satellite and environmental sensors. See:
https://news.mit.edu/2018/explained-detecting-threat-nuclear...
Update: Yes, this can be detected from satellite imagery:
http://www.princeton.edu/~aglaser/IT009-Glaser-2010-iGSE-New...
> The UN atomic watchdog certified the Iranians were following the deal until sometime after the U.S. pulled out.
Source?