WASHINGTON—The U.S. is pulling out of the Iranian nuclear accord, President Donald Trump announced Tuesday, dismantling his predecessor’s signature foreign-policy achievement and bucking the wishes of some of America’s closest allies.
Speaking in the Diplomatic Room of the White House, Mr. Trump delivered harsh words about the deal, calling it “horrible,” “one-sided” and “disastrous.” The president said he planned to institute “the highest level of economic sanctions” against Iran, and said the U.S. would sanction any nations that help Iran pursue nuclear weapons.
Administration officials said the Iran sanctions are immediately back in effect, banning new contracts and financial deals but giving businesses and banks either 90 or 180 days to wind down existing ties, depending on the particular type of transaction.
“The Iran deal is defective at its core,” Mr. Trump said. He cited Israeli Prime Minister Benjamin Netanyahu’s announcement last month of what he called new evidence that Iran maintained a secret plan to build nuclear weapons but repeatedly lied about it.
“We have definitive proof that this Iranian promise was a lie,” Mr. Trump said. Many experts and former officials said the new evidence cited by Mr. Netanyahu provided no new information because the U.S., Europe and international nuclear inspectors have long held that Iran pursued a nuclear-weapons program until 2003 and that some of these activities continued as late as 2009.
U.S. intelligence officials, the United Nations’ nuclear watchdog and European allies have repeatedly said Iran was complying with the accord.
The president said he “engaged extensively” with allies and partners in recent months, including France, Germany and the U.K. “We are unified in our understanding of the threat,” he said. French President Emmanuel Macron last month urged Mr. Trump not to withdraw from the accord.
Mr. Trump said his decision to withdraw from the pact signaled that “the U.S. no longer makes empty threats.”
“When I make promises, I keep them,” he said.
The president said he was “ready, willing and able” to negotiate a “new and lasting deal” with Iran. “Great things can happen for Iran, and great things can happen for the peace and stability that we all want,” he said.
At the same time, he issued a warning to Tehran: “If the regime continues its nuclear aspirations, it will have bigger problems than it has ever had before.”
The president cast in dire terms the need for the U.S. to withdraw from the accord. “If I allowed this deal to stand, there would soon be a nuclear arms race in the Middle East,” he said.
Mr. Trump was joined for the announcement by Vice President Mike Pence, national security adviser John Bolton and Treasury Secretary Steven Mnuchin.
Before his announcement, the president called some foreign leaders to inform them of his decision, while Vice President Mike Pence was on Capitol Hill on Tuesday explaining the decision to key members of Congress.
A parade of European leaders has come through Washington in recent weeks to urge Mr. Trump not to abandon the accord. French President Emmanuel Macron late last month warned that doing so would “open Pandora’s box” in the absence of a follow-on plan. German Chancellor Angela Merkel reinforced that message days later on her own visit with Mr. Trump, describing the Iranian nuclear deal as a “building block” and part of a “mosaic” needed to contain Tehran.
On Monday British Foreign Secretary Boris Johnson made a last-minute appeal to save the accord, including meetings with Vice President Mike Pence and Secretary of State Mike Pompeo, and an appearance on one of Mr. Trump’s favorite television programs, “Fox & Friends.”
In those discussions Mr. Johnson acknowledged some of Mr. Trump’s criticism of the accord, which limits and monitors Iran’s nuclear activity but doesn’t restrain its ballistic-missile program or its support for regional foes of the U.S. such as Hezbollah and Syrian President Bashar al-Assad.
“We need to find a way of fixing that and the president has been right to call attention to it,” Mr. Johnson said on Fox. “But you can’t do that without just throwing the baby out with the bath water.”
—Byron Tau and Ian Talley contributed to this article
Write to Michael C. Bender at Mike.Bender@wsj.com and Rebecca Ballhaus at Rebecca.Ballhaus@wsj.com