Tillerson acknowledges 'disagreements' with Trump over Iran nuclear deal

US Secretary of State Rex Tillerson on Tuesday acknowledged that he and President Donald Trump disagree over the 2015 Iran nuclear deal, just days after the US imposed new sanctions on the country in late July.

The nuclear deal, signed in 2015 by Iran and six powers including the United States, led to the lifting of most sanctions against Tehran in return for curbs on its nuclear programme.

"He and I have differences of views on things like JCPOA, and how we should use it," Tillerson said at a State Department briefing, using the acronym for the Iran deal formally called the Joint Comprehensive Plan of Action (JCPOA).

Last week, Trump issued a veiled threat against Iran, warning Tehran to adhere to the terms of the nuclear accord or face "big, big problems."

During his election campaign he denounced the agreement reached under former president Barack Obama as the "the worst deal ever" and promised to get tough on Iran.

Trump has now twice affirmed Iran's compliance since taking office, however, effectively keeping the deal in place.

"There are a lot of alternative means with which we use the agreement to advance our policies and the relationship with Iran, and that's what the conversation generally is around with the president as well," Tillerson said in Tuesday’s comments.

The US official acknowledged that the United States is limited in how much it can pressure Iran on its own and said it was important to coordinate with other parties to the agreement.

"The greatest pressure we can put to bear on Iran to change the behaviour is a collective pressure," he said.

Washington could "tear it up and walk away" or stay in the deal and hold Iran accountable, he added.

The White House did not immediately respond to a request for comment on Tillerson's remarks.

The US Treasury's Office of Foreign Assets Control imposed sanctions on six Iranian firms in late July for their role in the development of ballistic missile programme after Tehran's launch of a rocket capable of putting a satellite into orbit.

Iran on Tuesday complained to the UN Security Council about sanctions, saying they breached Tehran's nuclear deal with major powers.