OpenSea said in a statement that "OpenSea blocks users and territories on the U.S. sanctions list from using our services", though it's unclear why this change seems to only have come into effect recently.
Iranian users were surprised to find that their OpenSea accounts had been deactivated with no warning. One Iranian user wrote, "NOT A gm AT ALL. Woke up to my opensea trading account being deactivated/deleted without notice or any explanation, hearing lots of similar reports from other Iranian artists & collectors. What the hell is going on? Is OS straight up purging its users based on their country now?" At least one user who reported issues said that they are Iranian, but haven't lived there in years, and are based in Italy.