(CNN) President Donald Trump on Friday threatened to pull out of a deal freezing and reversing Iran's nuclear program if Congress and US allies do not agree to strengthen it, as he unveiled a tough and comprehensive new policy toward the Islamic Republic.

"As I have said many times, the Iran deal was one of the worst and most one-sided transactions the United States has ever entered into," Trump said in a major speech at the White House.

In effect, Trump put the agreement in limbo without killing it off entirely as some backers had feared. But his strategy risks setting off a chain of unpredictable consequences that could end up derailing the deal anyway and eventually raise the risk of war between the US and Iran.

Trump accused Iran of committing "multiple violations of the agreement," despite the fact that the International Atomic Energy Agency, America's European allies and even his own government say that Tehran is complying with the 2015 deal agreed by former President Barack Obama and major world powers.

He said that Iran had "failed to meet our expectations in its operations of advanced centrifuges," and "intimidated" international inspectors into not using their full authority. He also accused the Obama administration of lifting sanctions on Iran under the terms of the deal at a moment when the Iranian clerical regime was about to collapse, an assessment that contradicts the views of many experts. He also ordered US intelligence agencies to mount a new assessment of Iran's compliance.

The President announced that he would no longer make regular certifications that the lifting of sanctions under the deal had been in US interests.

"We cannot and will not make this certification. We will not continue down a path whose predictable conclusion is more violence, more terror and the very real threat of Iran's nuclear breakout," he said. "I am directing my administration to work closely with Congress and our allies to address the deal's many serious flaws so that the Iranian regime can never threaten the world with nuclear weapons."

He said the deficiencies of the agreement included "sunset" provisions under which limits on Iran's nuclear program will begin to expire. Proponents of the deal dispute that.

The President warned that the deal was plagued by "insufficient enforcement" and near total silence on the missile program. The Obama administration deliberately excluded other deep disagreements with Iran from the deal, reasoning that its threat would be much worse if he was able to quickly race to a nuclear weapon in a matter of months.

Trump warned that if he did not get the changes he wanted, he would unilaterally kill the deal.

"In the event we are not able to reach a solution working with Congress and our allies, then the agreement will be terminated. It is under continuous review and our participation can be canceled by me as President at any time."

The comment appeared to be a classic negotiating gambit by Trump, leaving other parties to the deal in no doubt that he is ready to walk out to get better terms. Given the deep reluctance of the Europeans, Russia and China and Iran to reopen the agreement, his approach is a high-risk one. Still, if he were to later back down, it would not be the first time that Trump has spelled out a tough stance on the campaign trail or in a political speech and ultimately moderated his stand.

The administration wants to include new sanctions in US law that would snap into place should Iran continue to launch ballistic missiles or refuse to extend restrictions on its uranium enrichment when the deal expires in eight years time. European powers have said they are open to negotiating separate deals with Iran but do not favor anything that would endanger the original agreement. Iran has warned against any action that could be seen as renegotiating the 2015 deal retroactively, but it is not clear if it would regard the new sanctions the administration is pushing as a violation of the deal.

As Trump spoke, the Treasury Department issued a statement saying that it would designate Iran's Islamic Revolutionary Guard Corps for new sanctions over its support for terrorist organizations throughout the Middle East. It did not, however, single out the powerful militia as a foreign terror organization through the State Department. Earlier, the head of the Atomic Energy Organization of Iran, Ali Akbar Saleh, warned that terming the guards as a terror group would be "tantamount to a declaration of war."

Friday's action "should not be misconstrued as a compromise," said a Treasury spokesperson in a statement, who referred questions to the State Department on its own designation process.

Trump's comments went a lot further than senior aides, including Secretary of State Rex Tillerson, had suggested. While Trump's move sends the deal's fate to Congress he did not rip up the agreement. Tillerson had suggested that if Congress does not agree to impose new sanctions on Iran the deal would remain in place. But Trump's warning that he could terminate the agreement appeared to call that into question.

Iran's President Hassan Rouhani, who has significant political capital invested in the deal, made a live address soon after Trump spoke, saying that the US President could not decide the fate of the deal on his own.

"This is an international, multilateral deal that has been ratified by the UN Security Council. It is a UN document. Is it possible for a President to unilaterally decertify this deal? Apparently, he's not in the know."

Trump had been weighing his Iran decision for weeks and faced intense pressure from European allies to maintain the US commitment to the accord. His national security advisers had encouraged him to avoid completely withdrawing from the agreement, which was signed by the US along with Britain, France, Germany, Russia, China, the European Union and Iran in 2015.

A complete removal of the United States from the nuclear deal would isolate the United States and provide an opening for Iran to rethink its own commitments on reducing nuclear stockpiles, some of Trump's advisers and foreign counterparts warned.

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Fulfills top campaign pledge

Trump has resisted, insisting that he fulfill a core campaign promise to remove the United States from agreements he deems poorly negotiated and harmful. He has twice "certified" the deal, but angrily told his top advisers that he would do so no longer, fearing it appeared he was backing out of his pledge.

Trump made known in "forceful, not uncertain" terms that he was disappointed by the options his team had been presenting him and wanted a different approach, according to a person familiar with the discussions, who described Trump's reaction as an "extended outburst." The confrontation came around July 17, when he last certified Iran's compliance in the deal.

Trump was upset and -- in the face of other unfulfilled campaign promises -- angry that his team appeared to be steering him away from one of his chief pledges to voters.

According to the source, Trump complained that his national security team, including Tillerson, Defense Secretary James Mattis and National Security Adviser H.R. McMaster, didn't feel as much urgency in completing something he had promised to do on the campaign trail.

He certified the deal over the summer, but continued to resent his top aides for pressuring him to do it, the source said. He later stated publicly in an interview that he would rather have decertified the agreement.

Since then, Trump's team devised the middle-of-the-road plan that he unveiled Friday, which allows the President to proclaim to supporters that he's rejected the deal while still remaining a party to it. All of his national security team, at this point, is behind the decision, according to senior administration officials.

"The President, on many occasions, talked about either tearing the deal up or fixing the deal, and he said many times, we got to fix this deal," Secretary of State Rex Tillerson told reporters on Thursday evening. "What we are laying out here, this is the pathway, we think, that provides us with the best platform to attempt to fix this deal."

"We may be unsuccessful, we may not be able to fix it and if we are not, then we may end up out of the deal," Tillerson went on. "But I think what the President is saying, before I do that and just walk, look, we will try. We will try. We will go try to fix it. I think you are going to hear he is not particularly optimistic."

Iran's Speaker of Parliament Ali Larijani said Friday that Iran may withdraw from the nuclear agreement if the United States does, Russian state-run TASS reported Friday.

Speaking to reporters in St. Petersburg, Larijani acknowledged that quitting the deal was "a possibility" and said that if the US does not implement the agreements reached when the nuclear deal was signed, nothing will remain of the accord.

"If they act like it, then there will be hardly anything left from this agreement. So a new issue will arise on the international arena," Larijani said, according to Russia's state-owned outlet Sputnik

Kremlin spokesman Dmitry Peskov said Friday that it was "obvious" that any action by the US to pull out of the Iran nuclear deal will have "very, very negative consequences."

In telephone conversations with French President Emanuel Macron and British Prime Minister Theresa May this week, Trump heard sharp resistance to any move that would weaken the Iran nuclear deal. Both leaders affirmed their countries' commitments to remaining part of the accord.