Looks to me like the target for their first nuke is the oil loading facilities in Saudi Arabia, particularly if combined with a dirty bomb to slow down rebuilding.
They achieve three objectives with this move: a western economic panic, a split in the west between appeasers and defenders, and an increase in their own oil profits.
Heard some Aussie comentator on the radio Monday night, a supposed expert on Iran, who said it is not inconceivable that the Israelis would launch a preemptive nuclear strike against the Iranian facilities, if it is determined that conventional weapons won't do the job. Things could get very interesting.