The majority of comments on here seem to be concentrating on the Iranian Kilo's and the Iranian fast attack craft.
KILO's - Are indeed very hard to detect. However, once you've got your 'claws' into them, it's not too difficult to hang on. If the 2 currently assessed to be at sea were to suddenly 'disappear' the finger may well be pointed at the USA but where would the proof be? As a consequence, if things did hot up dramatically, I wouldn't be at all surprised to see them disappear off the Iranian ORBAT within minutes.
Fast Attack Boats - Make a lot of noise. The US Navy would see them coming acoustically from miles away. Any 'swarm' may be hard to deal with but could be feasibly overcome all the same (IMHO).
What if the US Navy simply enforced a blockade on Iranian naval assets thereby denying any (or further?) mining operations? If the Ianians then decided to militarily counter these efforts, I'm sure the US assets could adequately reply.
It's the potential nuclear threat we should be worried about....