WASHINGTON: US Secretary of State Rex Tillerson will "very shortly" make an announcement on Iran's nuclear agreement with world powers that President Donald Trump has called a "bad deal," White House spokesman Sean Spicer said on Monday.

Under US law, the State Department must notify Congress every 90 days of Iran's compliance with the 2015 deal. Monday is the deadline, and a senior US official said last week the administration was very likely to say Iran was adhering to the agreement although Trump has reservations about it.

"The secretary of state will have an announcement very shortly on that deal," Spicer told reporters. "I think you all know that the president has made very clear that he thought this was a bad deal, a bad deal for the United States."