Trump warns Iran to comply with nuclear deal or face 'big problems'

US President Donald Trump issued a veiled threat against Iran on Tuesday during a rally, warning Tehran to adhere to the terms of a nuclear deal with world powers or else face "big, big problems".

A week after certifying Iran as complying with the 2015 agreement negotiated by Democratic President Barack Obama, Trump made clear to thousands of raucous supporters that he remains extremely wary of Tehran.

Trump administration officials, briefing reporters last week, said new economic sanctions against Iran were being prepared over its ballistic missile programme and for contributing to regional tensions.

Trump devoted part of his rally in Youngstown, Ohio, to Iran.

"If that deal doesn’t conform to what it’s supposed to conform to, it's going to be big, big problems for them. That I can tell you. Believe me," Trump said.

"You would have thought they would have said 'thank you United States. We really love you very much.' Instead, they've become emboldened. That won’t take place much longer," he said.

Trump told the Wall Street Journal on Tuesday he would be surprised if Iran is in compliance with the nuclear deal when recertification comes up again in three months.

"We’ll talk about the subject in 90 days but I would be surprised if they were in compliance," he told the Journal in an interview.

According to a Reuters report published on Monday, Trump was not fully on board with recertifying the nuclear deal and internally criticised his Secretary of State Rex Tillerson over backing the accord.

Trump used his speech to revisit some of the themes that helped him to his improbable victory in the presidential election in November.

He railed against "radical Islamic terrorists" and vowed he wanted to keep them from entering the United States after the "total devastation" he said they had caused in Europe.

"We only want to admit those into our country who share our values," Trump said.

Throughout the crowd were reminders of the campaign from chants of "drain the swamp" to "CNN sucks".

Several protesters were ejected, including a youth waving a Soviet-style flag. "Boy, he's a young one," Trump said. "He's going back home to mommy. And I bet mommy voted for us."