What kind of monitoring are you thinking? Uranium is primarily an alpha emitter, and as such very easy to shield. I don't think it could be tracked from a distance.
We had cameras and other devices installed under the old nuclear deal.
https://www.nbcnews.com/politics/national-security/iran-remo...
> It appeared Iran intended to remove the bulk of the cameras and other monitoring gear installed as part of the 2015 nuclear agreement between Tehran and world powers, according to Grossi. Without cameras in place, Iran could divert centrifuges used for uranium enrichment to other unknown locations, he said.
Maybe antineutrinos. There has been a fair bit of work on detectors in the past couple of decades.
Those are for detecting nuclear reactor antineutrinos, to monitor plutonium-producing reactors associated with weapons programs. Not a pile of uranium sitting around doing nothing.
Trump canceled the deal that included monitoring. The Iranians, as you’d expect, disabled those in response.
https://en.wikipedia.org/wiki/United_States_withdrawal_from_...
Surveillance UAVs exist, loiter indefinitely, and Israel has declared air superiority from the beginning.
I’m sure they aren’t telegraphing capabilities, but aren’t monitoring devices trained on iran nuclear sites that have been in place for decades.
The intelligence value alone of knowing where materials are going would be so valuable that this has to be in place.