Well it definitely helps to have evidence. And now-a-days it should be exceptionally hard to get or make a nuclear bomb without it being known about...unless Iran is lying, and isn't just enriching Uranium for power.
I still don't think they'd use a Nuclear bomb at this stage. It's just too severe a thing to do. The consequences would be catastrophic. A dirty bomb would be the most logical thing, or something containing Ricin or Anthrax.
Fine. They only hate America, they have nothing against any one else, really. My parents were actually just down their, and they said it was very welcoming and awesome.