While the US State Department was obliged to admit that Iran remains in full compliance with the P5+1 nuclear deal in a report to Congress, they are clearly not happy about that fact, and with President Trump openly looking to "renegotiate" the deal, Secretary of State Rex Tillerson attacked the pact in general.
Indeed, Tillerson's comments gave the appearance he didn't know about the compliance, even though he was the one who signed the letter in the first place, as he attacked the P5+1 deal as a failure and accused Iran of "unchecked" nuclear ambitions posing a grave risk to the world.
Iran was never particularly close to nuclear weapons, and its leadership has repeatedly ruled out developing them. The P5+1 deal allows Iran an extremely limited civilian nuclear program, and since its implementation both the US and IAEA have repeatedly affirmed Iranian compliance.
Which means if the US wants to weasel its way out of the deal, which they clearly do, they need to invent some other problem, with Tillerson claiming that Iran's status as a "state sponsor of terrorism" could justify backing out of the deal.