Iran is wary of the fact that Israel has nukes. It only takes one to end the war. And Israel is too insane to not launch it. The government of Israel is filled with complete fanatics.
I just hope Iran is building a dirty bomb with their enriched uranium. Fine, they won't get a clean nuke anytime soon, but then if they get nuked, they have to respond with a dirty bomb that renders Jerusalem or something uninhabitable for a thousand years.