The deal, Trump said, is no longer in the national security interest of the United States. This decision, which has been referred to as “decertification,” is a shift in official position.
It is a significant declaration that leaves the nuclear agreement in place, but puts Congress in charge of whether or not to follow up with action -- triggering a 60-day window for lawmakers to re-impose sanctions against Iran that were suspended in 2015 as part of the agreement.
Trump outlined three steps as part of America's path forward: to counter "destabilizing activity" in the Middle East, impose new sanctions on non-nuclear aspects of the regime and address the country's nuclear ambitions.
"Our policy is based on clear assessment of Iranian dictatorship, its sponsorship of terrorism and its continuing aggression in the Middle East and all around the world," Trump said.
While the president portrayed the decision as having originated with his administration, he acknowledged that Congress holds the key to the deal's future.
"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.
Tehran and world powers in July 2015 crafted a deal that eased sanctions on Iran in exchange for stepped-up international monitoring of its nuclear development activities.
The agreement reduced the amount of nuclear fuel Iran can keep and extended the "breakout time" needed for Iran to create a single bomb. Some of Iran's facilities are now also subject to constant monitoring, with others subject to inspections after a waiting period.
The president accused Iran of "not living up to the spirit of the deal," while the U.S. abides by its promises, despite top officials on his national security team, including Defense Secretary James Mattis, saying Iran has technically complied with its restrictions. The International Atomic Energy Association, tasked with validating Iran's adherence to the agreement, released a statement Friday further confirming the country's compliance.
"At present, Iran is subject to the world's most robust nuclear verification regime," the IAEA said in a statement.
Trump's remarks, while not alleging a specific violation of the nuclear-related terms, singled out the "Iranian regime" for "continu[ing] to fuel conflict, terror, and turmoil throughout the Middle East and beyond."
Iranian President Hassan Rouhani defended his country's participation in the deal Friday after Trump's speech and attacked the decision, saying that the U.S. was "completely alone" in its policy toward Iran. He added that Iran would not hesitate to respond if the deal's other parties "do not stay loyal."
Rouhani further characterized Iran’s missile program as purely defensive in nature and necessary in the face of U.S. aggression.
“We always tried to produce weapons ourselves,” he said. “And from now on we will redouble that effort... to defend ourselves.”
In a series of tweets Friday afternoon, Iran's Foreign Minister Javad Zarif portrayed Trump as kowtowing to external interests, and describing the U.S. president's words as "rogue."
Trump also announced sanctions Friday on Iran's Revolutionary Guard Corps, whom he accused of providing assistance to terrorist groups. He encouraged U.S. allies to take action to counter the group's efforts "including thorough sanctions outside the Iran deal that target the regime's ballistic missile program in support for terrorism and all of its destructive activities, of which there are many."
Though Trump did not go so far as to end the nuclear deal, he told reporters on the White House South Lawn after his speech that his prior threat to "rip it up" was still a possibility.
"I may do that. I may do that," Trump said. "The deal is terrible. So what we've done is, through the certification process, we'll have Congress take a look at it and I may very well do that. But I like a two-step process much better."
Republicans critical of the initial deal have urged the administration to enforce it.
Sen. John McCain, R-Ariz. said in a statement Friday that he agrees with Trump that the deal doesn't benefit U.S. interests, but that he is interested in approving, rather than ending, it.
"I look forward to working with my colleagues in Congress on additional legislation to increase sanctions and other pressure to hold Iran accountable for its broader destructive behavior in the region," McCain said in the statement. "I am also eager to collaborate with our partners and allies to revisit the most problematic provisions of the nuclear deal, and support a unified, forceful international front in the event that Iran materially breaches the terms of the agreement."
On Wednesday, House Foreign Affairs Committee Chairman Ed Royce, R-Calif. said in a hearing that while he felt the deal was "flawed," he believed the U.S. "must now enforce the hell out of it."
“Let’s work with allies to make certain that international inspectors have better access to possible nuclear sites, and we should address the fundamental sunset shortcoming, as our allies have recognized," said Royce.
The goal with such actions, according to Cotton, would be to bring Iran back to the negotiating table to strengthen the original deal.
But some Obama-era officials who worked on the agreement said that hope was unrealistic.
“I would love to see Iran come back to the table, apologizes for everything and agree to all of our demands,” Philip Gordon, White House coordinator for the Middle East during the Iran negotiations, told ABC News. But he called such a notion a “fantasy.”
Former Secretary of State John Kerry, a signatory to the agreement who personally engaged in the final negotiations, released a highly critical statement after Trump's speech Friday. Kerry called Trump's decision a "dangerous" on that "polluted the negotiating waters," and expressed bewilderment at why the president would not recognize Iran's adherence to the terms. He called on Congress to follow through in maintaining the spirit of the deal.
"Our allies and our Congress must now act as the only adults left in the room with the power to protect our national interests," the statement read, in part, adding, "I can't think of a more important moment than this one where cooler, wiser voices have had a bigger responsibility to put a policy back on track."
“You can only tear these things up one time. It might feel good for a second, but one of the things that's important for us is to keep our allies with us,” he said, referring to the other signatories of the Iran deal which include China and Russia as well as the European Union.
While many of the parties to the deal spoke out against Trump's stance, the president found supporters in a pair of regional allies who were not signatories to the agreement: the United Arab Emirates and Saudi Arabia. The latter described the U.S.'s strategy Friday as "resolute" and a "clear-eyed vision."
Both the UAE and Saudi Arabia are considered regional rivals of Iran and have made overtures to work towards a closer relationship with the Trump administration since the president's inauguration in January. Each country expressed public support for the nuclear deal upon its signing, despite reservations.
ABC News' Conor Finnegan, Kirit Radia and Benjamin Siegel contributed to this report.