Earlier: President Donald Trump is delivering a speech on the Iran nuclear accord, which he has repeatedly denounced as the worst deal in American history.
Mr Trump will not withdraw from the deal or reimpose sanctions, but he will say the pact is not in national security interests, US secretary of state Rex Tillerson has said.
The plan would allow Mr Trump to keep up his criticism of the deal, while also reassuring US allies that Washington will not walk away from it, at least not immediately.
In his speech, Mr Trump will notify Congress that he is "decertifying" the deal, known as the Joint Comprehensive Plan of Action, arguing that while Iran may be complying with the letter of the agreement, the accord itself is not sufficient to be in US interests.
In remarks ahead of his address to a group of conservative voters, Mr Trump previewed his position by calling Iran "a terrorist nation like few others" and urged his audience to listen to the speech.