Seymour Hersh has written an article for the New Yorker entitled "The Iran Plans". He seems to have spoken to quite a number of (unnamed) insiders who confirm that detailed planning for an attack on Iran is going ahead and that it is likely that tactical nuclear weapons might be used. He also claims that some top military officers are close to resigning over the plan to use tactical nuclear weapons.

The article is here:
http://www.newyorker.com/fact/content/articles/060417fa_fact.

See also:
http://physics.ucsd.edu/~jorge/publicservice.html.