Remember those forged Niger uranium documents? And remember how nobody is saying much about who actually forged them? Well, I've long suspected that Ahmed Chalabi and his INC were somehow involved because of the amateurishness of the documents. (It was signed by dead people and other stuff way too stupid for the CIA or Mossad to do, and the INC had a vested interest in the forgery. Still, this doesn't totally exonerate the U.S. government. Dick Cheney and his office eagerly ate up the intelligence despite the CIA's repeated warnings that the documents looked fake.)

Now that Chalabi has been closely linked to Iranian espionage (this fact was also widely rumoured in the CIA for years and ignored by Cheney), it is quite plausible that Iran was responsible for the forgery together with Chalabi. For more circumstantial evidence, read this.