It seems to me that the US ( like the UK over Russia) is choosy as to whom they blame. I would not be surprised at Iranians fighting in Iraq. There are certainly lots of nations there and with the inclusion of Israelis....
The last "proof" of Iranian involvement was later shown to be nothing of the sort. It seems that Chechens for instance, do not count. Curious that. Still, I suppose there has to be given a reason for sending another carrier group to the Gulf.