I hope that, at the appropriate time, after the sanctions kick in — and they are brutal what we've put on Iran — I hope that they're going to come back and negotiate a real deal because I'd love to be able to do that but right now it's too soon to do that.

From here:

Speaking to reporters following a historic meeting with Kim, at which the regime's leader signed an agreement that appeared to commit tothe "complete denuclearization of the Korean Peninsula," Trump said he hoped relations could also improve, in time, with Iran.