I appreciate Captain Kidd's further research, providing the Al-Jazeera site (which I note is the .net, not the .com). I'm not up on nuclear forensics(? terminology?), but I think Swift's comments are probably accurate in that the actual use of a nuke was unlikely.
Still, here, http://www.sciam.com/article.cfm?art...9&chanId=sa003 , is a link I found to a Scientific American story in regards to a relevant U.S. policy shift, uncovered by the Federation of American Scientists. The time lag in the process of their Freedom of Information Act extraction results in policy being dated by about 4 yrs.
Perhaps, (as in maybe, conjecture, supposition, speculation, or I wouldn't actually put money on this, unless, maybe, you were to give me some tempting odds...) the original source for U.S./nuke attack story was a agent for U.S. hawkish interests, disseminating misinformation to see what regional political vectors of anti-nuke sentiment could be drawn out to better prepare as the Iran response rhetoric escalates.
Perhaps the military only complied with F.A.S.'s F.I. request (something they could have probably gotten around or indefinitely prolonged), to send a subtle warning to Iran.
Perhaps not.
I notice with all the interesting talk in this thread of variation in yield and differing forms of delivery devices, there's been no mention of the somewhat controversial development in the last few years regarding the U.S. pursuing research into lower yield nukes.