This looks like a move to signal that the United States will be cautious on Iran, despite the new deal. State dept. officials argued that since Iran has not endorsed the geneva convention the US cannot support their inclusion in these talks. This point makes plenty of sense to me. Secretary-General Ban Ki-moon, whose decision to invite Iran had threatened to unravel the Syria talks less than 48 hours before the scheduled start, issued a statement on Monday rescinding the invitation. The United States had said it was surprised by the invitation because Iran had not agreed to conditions for the talks, to be held on Wednesday in Montreux, Switzerland.