Says the US Department of the Treasury, as mentioned in the Twitter thread further down:
> 118. I have a client that is in Iran to visit a relative. Do I need to restrict the account?
> No. As long as you are satisfied that the client is not ordinarily resident in Iran, then the account does not need to be restricted.
from their "FAQs: Iran sanctions" page — https://home.treasury.gov/policy-issues/financial-sanctions/...