YOUNGSTOWN, Ohio - US President Donald Trump issued a veiled threat against Iran on Tuesday, 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 program and for contributing to regional tensions.

Trump devoted part of his speech 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.

Fresh from a rare legislative victory in Washington when the Senate voted to start a debate on repealing Obamacare, Trump called on Democrats to end their opposition to his efforts but doubted they would.

"It's time for Democrats to stop resisting. That's their term, resist, resist. They have to do finally what's right for the American people, but probably we'll do it ourselves," he said. 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 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.

Trump came to Ohio amid a simmering feud with his attorney general, Jeff Sessions, and facing a prolonged investigation into Russian meddling in the presidential election. He cast himself as an anti-establishment figure fighting entrenched special interests in Washington, a point that his wife, Melania Trump, stressed when she introduced him on stage.

"Washington has fought him every step of the way, but I know my husband and he will never give up," she 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."

Trump rejected criticism that he has a style as president that is not politically correct. He routinely draws criticism for his tweets.

"I'd say with the exception of the late great Abraham Lincoln, I can be more presidential than any president that’s held this office," he said. "But we have to move a little faster than that. We will never be beholden to the lobbyists or the special interests."

Meanwhile, Iran will reciprocate if the United States imposes new sanctions on it, president Hassan Rouhani said on Wednesday according to state media, casting further doubt over the outlook for the 2015 Iran nuclear accord.

The US House of Representatives voted on Tuesday to slap new sanctions on Iran, Russia and North Korea, although it was unclear how quickly the bill would make its way to the White House for President Donald Trump to sign into law or veto.

State media quoted Rouhani as citing a verse from the Holy Quran saying: "If the enemy puts part of their promises underfoot then we will also put part of it underfoot. And if they put all of their promises underfoot then we will put promises underfoot."

But he added: "The Holy Qurran also advises that if enemies are really pursuing peace and want to put enmity aside and act appropriately toward you, then you should do the same."

He said that parliament would take the initial steps in responding to any US moves and that any necessary further steps would also be pursued.

On Tuesday, Trump issued a veiled threat against Iran, warning it to adhere to the terms of the 2015 nuclear deal it signed together with world powers or else face "big, big problems." A week after certifying Iran as complying with the agreement negotiated by Democratic President Barack Obama, Trump has made it clear that he remains extremely wary of Tehran.

The Iranian side appears equally wary of Washington, with a senior Revolutionary Guards commander issuing a similar threat in return on Wednesday.

"The Trump government, more than before, should be cautious and precise with their military approach in the Islamic revolution environment," Brigadier General Masoud Jazayeri, deputy chief of staff of Iran's armed forces was quoted by the Tasnim news site as saying on Wednesday.

"We will confront any American mischief with a response that will make them sorry," he said.

The head of the Guards was quoted as saying last week that Washington should move its bases and avoid "miscalculations" over new sanctions against Tehran. The United States has bases in Qatar and Kuwait across the Gulf from Iran, while the US Fifth Fleet is based in nearby Bahrain.