It didn't take me long to find out how to make one of those IEDs that supposedly have to come from Iran. After all, there's always Wikipedia. Wiki has a neat short introduction here, with an even better photo of one. The idea is simplicity itself. Using the Misznay-Schardin effect, which states that as an explosive charge usually exerts force perpendicular to its surfaces, if it is contained on one or more sides the blast will be concentrated on the open side, you back the charge with something solid.
Then, you shape it so the front face forms a convex shape, and fit a sheet of copper to that shape. And, essentially, you're done. All you need is a stout steel cylinder, something like a compressed gas bottle, and an oxy-acetylene torch or similar. The backing could just be sand - widely available in Iraq, I believe - and the copper could be beaten into shape against something hard (like the curved bottom of the gas bottle) with a hammer. (There's an interesting USAF publication here.)
I don't see where I need the Iranian Revolutionary Guards' Corps so far.
Doing the first-class compressed gas version will be more complicated, as the seal must be airtight but not strong enough to keep the bang from going out the right end. A trigger - well, there are many ways of doing this, and let's leave it at that. We are reasonable people, right?
None of this is new. Misznay and Schardin were Nazi engineers. The IRA used various forms of IEDs, including ones with an IR trigger. Some say MI5 told them how to, whether to keep them from learning worse, or to track the spread of memes through the organisation I don't know. Even before that, the German extreme-leftists knew the art of EFP. The Rote Armee Fraktion assassinated Alfred Herrhausen, a director of Deutsche Bank, with an IR-triggered one in 1989, or at least somebody did.
There's a great story about IRA links to the Middle East in Robert Fisk's Pity the Nation. Fisk had thought the rumours were nonsense (he had, after all, been the Times's Northern Ireland correspondent through the worst of the troubles), until one day when he took cover from an Israeli artillery bombardment and found he was sharing the cover with a man he recognised. The last time he had seen him had been in Derry in 1972, and the man had then been an IRA Volunteer, like you ever stop.
So, there are multiple ways this nasty little craft could have reached Iraq. And there is no necessary reason for Iran - or any other Dr Evil - to be involved. And so says the LA Times.