It isn't the U.S. Iran is worried about.
Israel blew through Syria's air defenses like they weren't there. Most of the defenses didn't even spot them. This was Russian top-of-the-line equipment, and not too coincidentally, the same equipment Iran has been buying like there's no tomorrow.
Iran is a bit nervous about this, to say the least. So are other Russian arms customers, and Russia isn't too happy about their future sales prospects.