Updated at 6:36 p.m. ET
President Trump announced Tuesday that he has decided to exit a 2015 multinational agreement in which Iran agreed to limit its production of nuclear weapons material.
"I am announcing today that the United States will withdraw from the Iran nuclear deal," Trump said.
He said the U.S. will reimpose economic sanctions that were lifted as part of the U.S. commitments made in the deal.
The U.S. has been repeatedly waiving sanctions that curtail Iran's oil sales, but those sanctions waivers faced a Saturday deadline, prompting Trump's move Tuesday.
Trump made the announcement during a speech at the White House.
"The fact is this was a horrible one-sided deal that should have never, ever have been made," he said.
"It didn't bring calm, it didn't bring peace, and it never will," he also said.
Speaking in a nationally televised address, Iranian President Hassan Rouhani called Trump a "bothersome creature." Rouhani also said Iran would attempt to hold talks with the other world powers in the deal to see whether the agreement can be continued. But if it can't, he said, Iran's atomic energy organization is prepared to restart nuclear activities.
Also speaking in a televised address, Israeli Prime Minister Benjamin Netanyahu said Trump's withdrawal from the nuclear agreement is historic. Netanyahu thanked Trump for his "courageous leadership" and "commitment to confront the terrorist regime in Tehran."
In a statement, Saudi Arabia said it "supports and welcomes the steps announced" by Trump. "The Kingdom also supports reinstating economic sanctions on the Iranian regime."
Trump's repudiation of the agreement was called "misguided" by former President Barack Obama, whose administration negotiated it. In a joint statement, the leaders of Great Britain, France and Germany, which all signed the agreement, expressed "regret and concern."
Speaking slowly and deliberately, Trump did not mention his predecessor by name but clearly had the Obama administration in mind.
Trump called the agreement, which was drafted along with U.S. allies, "poorly negotiated."
The president also said that at a time when the U.S. "had maximum leverage, this disastrous deal gave Iran many billions of dollars, some of it in actual cash," which Trump called "a great embarrassment to me as a citizen and to all citizens."
"It is clear to me that we cannot prevent an Iranian nuclear bomb under the decaying and rotten structure of the current agreement," Trump said, calling it "defective at its core."
Trump justified his decision by citing what he sees as flaws in the deal. He called the sunset provisions of the agreement, which allow Iran to resume its nuclear enrichment program when the agreement phases out by 2030, "totally unacceptable." If allowed to stand, he said, the agreement would spark a nuclear arms race in the Middle East. "Everyone would want their weapons ready by the time Iran had theirs," the president warned.
Trump also criticized the agreement's inspection provisions, which he called inadequate, and its failure to prevent Iran from building ballistic missiles capable of delivering a nuclear warhead.
In a statement, Obama, who rarely addresses actions of his successor, said the agreement is working and "has significantly rolled back Iran's nuclear program."
Walking away from it "turns our back on America's closest allies," the former president said.
Obama added, "In a democracy, there will always be changes in policies and priorities from one Administration to the next. But the consistent flouting of agreements that our country is a party to risks eroding America's credibility, and puts us at odds with the world's major powers. Debates in our country should be informed by facts, especially debates that have proven to be divisive."
Trump said he consulted extensively with U.S. allies in Europe and in the Middle East. "We are unified in our understanding of the threat," Trump said, "and in our conviction that Iran must never acquire a nuclear weapon."
The path ahead is unclear. In their statement, British Prime Minister Theresa May, French President Emmanuel Macron and German Chancellor Angela Merkel urged the U.S. to "do everything possible to preserve the gains for nuclear non-proliferation brought about" by the agreement "by allowing for a continued enforcement of its main elements."
The leaders also encouraged Iran "to show restraint in response to the decision by the US; Iran must continue to meet its own obligations under the deal, cooperating fully and in a timely manner with IAEA inspection requirements."
The three European leaders also said they remained committed to the agreement. "We urge all sides to remain committed to its full implementation and to act in a spirit of responsibility," the trio said.
After his remarks, Trump signed a presidential memorandum that he said reinstates "the highest level" of economic sanctions on Iran and said any nation that helps Iran in its quest for nuclear weapons could also face sanctions.
Trump also declared Tuesday that "America will not be held hostage by nuclear blackmail."
The president added that his action "sends a critical message" that the U.S. "no longer makes empty threats." Instead, Trump explained, "when I make promises, I keep them."
Trump also announced that Secretary of State Mike Pompeo was on his way to North Korea for talks in preparation for a planned summit between Trump and North Korean leader Kim Jong Un. "Plans are being made, relationships are building, hopefully a deal will happen," Trump said.
The top Democrat on the Senate Foreign Relations Committee criticized Trump's decision to withdraw from the Iran pact.
"With this decision President Trump is risking U.S. national security, recklessly upending foundational partnerships with key U.S. allies in Europe and gambling with Israel's security," Sen. Bob Menendez, D-N.J., said in a statement. "Today's withdrawal from the [deal] makes it more likely Iran will restart its nuclear weapons program in the future."
"The governments of Iran, Russia, and China will seize this opportunity of self-imposed U.S. isolation to continue major weapons sales, deepen economic ties, and further challenge the United States and Europe not only in the Middle East but in other areas like North Korea," Menendez also said.
Republicans praised Trump's action. House Speaker Paul Ryan, R-Wis., said that "the Obama-era agreement" was "deeply flawed" and that Trump's announcement was "as strong statement that we can and must do better."
House Minority Leader Nancy Pelosi, D-Calif., responded on Twitter with a substantial thread of criticism of the president's decision.
Trump faced a May 12 deadline to decide whether to continue to waive certain sanctions that would prevent countries or companies from buying oil from Iran. Imposing the sanctions would effectively breach the deal.
The president has repeatedly bashed the Iran nuclear agreement, calling it one of the worst deals he has ever witnessed. During his presidential campaign, Trump had promised to "dismantle the disastrous deal with Iran."
The 2015 agreement with Iran was negotiated by the Obama administration and signed by the U.S., U.K., France, Germany, China and Russia.
As a part of the deal, Iran agreed to limits on its nuclear weapons program and ongoing inspections in return for relief from economic sanctions.
Critics of the deal argue that it gave away too much without addressing other critical issues, including Iran's development of ballistic missiles and its support of destabilizing actions in the Middle East.
There are also concerns that certain provisions of the deal are not permanent, potentially allowing Iran to restart its nuclear program.
After entering office, Trump continued to have harsh words for the deal, but he had stopped short of actually pulling the United States out of the agreement.
There were disputes in the White House and the Cabinet about how to handle the Iran deal. Former Secretary of State Rex Tillerson and former national security adviser H.R. McMaster both backed staying in the agreement, a view that put the officials at odds with Trump.
European allies had urged the president to stick with deal, despite his misgivings. Macron, who was treated to an official state visit at the White House last month, said the agreement could be kept in place while the countries work to craft a new and more comprehensive pact.
Even some opponents of the deal in Congress said it would be best to remain in the agreement until something better was put in place.
"I believe the best path forward at this point is to continue pushing to fix these flaws as we enforce the hell out of the deal," said Rep. Ed Royce, R-Calif., the head of the House Foreign Affairs committee, in a statement before Trump's announcement.