Israeli Prime Minister Benjamin Netanyahu presented what he called new evidence that Iran maintained a secret and comprehensive plan to build nuclear weapons but lied repeatedly about it, building a case against the 2015 Iran nuclear deal.
The broadside by Mr. Netanyahu on Monday, broadcast in Israel and the U.S., came as President Donald Trump nears a May 12 deadline to decide whether to withdraw from the deal, which halted Iran’s nuclear program in exchange for economic benefits. Mr. Netanyahu said the agreement was a mistake and urged Mr. Trump to do “the right thing.”
Mr. Netanyahu said the documents obtained by Israel, which he said included 100,000 files on paper and discs, show that “Iran is brazenly lying when it says it never had a nuclear weapons program.”
Mr. Trump said later that he agreed the 2015 nuclear agreement was a mistake, adding it would allow Iran to resume nuclear activities in seven years.
“That is just not an acceptable situation,” Mr. Trump said at a news conference with Nigeria’s president, after he was asked about Mr. Netanyahu’s presentation.
“I’m not telling you what I’m doing” with regard to the May 12 deadline, he said.
Iran’s lead negotiator in the talks leading to the 2015 nuclear deal told Iranian state television that Mr. Netanyahu’s presentation was “a childish, ridiculous show.”
The documents he presented were counterfeits, said the official, Abbas Araghchi, describing claims about a hidden stash of documents as laughable.
“How would Iran keep such important documents in a deserted industrial warehouse?” he said. “The fact that Netanyahu performs this show 10 days before Trump’s decision on the JCPOA makes it clear that it is an orchestrated play to influence Trump’s decision,” he said.
Iran has denied it was seeking to build nuclear weapons, although many U.S. and international officials have long believed the country’s Islamic government was attempting to do so at one time.
As part of the 2015 nuclear deal, the United Nations’ nuclear watchdog conducted a probe of Iran’s previous nuclear work. That investigation was finished in December 2015 and found no credible evidence that Tehran had engaged in recent atomic-weapons activity. But the agency reported that the country had pursued a program in secret until 2009.
Mr. Netanyahu in his comments claimed to have new evidence of Iran’s prior weapons program, displaying replicas of binders and CDs that he said were part of secret files from a bunker in Tehran. He said that Iran’s false denials represented a violation of the 2015 agreement.
Mr. Trump set a May deadline to decide whether to leave the deal. He has said he would pull out unless Europe agrees to address his concerns with Iran’s ballistic missile program, limits on Iran’s nuclear program that begin to expire in 2025 and the inspections regime detailed in the agreement.
The Israeli leader’s comments came a day after meeting with U.S. Secretary of State Mike Pompeo in Tel Aviv.
Messrs. Netanyahu and Trump spoke by telephone on Saturday, the White House said.
Mr. Netanyahu said the U.S. has vouched for the authenticity of the materials uncovered by Israel and has shared the documents with the U.S.
“We have not seen everything, but they have been very eager to share it with us,” a White House official said. “We have no reason to think that anything is inauthentic.”
Israeli officials have been discussing the files with American officials in recent days, the official said, suggesting the release was a coordinated effort. “We were not unhappy about it,” the White House official said of the presentation.
The Trump administration was impressed by the “volume and completeness of the picture” of Iran’s work that the materials presented, the official said.
However, U.S. intelligence officials and Mr. Pompeo have said that Iran is in compliance with the 2015 agreement, concurring with a view advanced by European officials and nuclear inspectors.
Mr. Netanyahu has lobbied furiously against the nuclear agreement since before it was reached, speaking against it in an address before the United Nations and in a speech to the U.S. Congress in 2015 that drew controversy because the Israeli leader and GOP congressional leaders arranged it, going around the White House, contrary to protocol.
The Trump administration is seeking what it has described as improvements to the 2015 deal between six world powers and Iran. It is trying to enlist Saudi Arabia and other regional powers to contribute more to confronting Iran in the region.
The Trump administration believes the deal gives Iran too much in sanctions relief in exchange for too few curbs on Iran’s nuclear program.
The Israeli leader argued that the files proved Iran had lied about its nuclear ambitions before signing the deal in 2015, and that Iranian attempts to keep the plan secret indicated Tehran was waiting for a time of its choice to use nuclear weapons.
He showed photos and documents documenting “Project Amad,” engineering and design work on weapons and the nuclear core of a warhead. He said officials who were in charge of the country’s weapons efforts would one day be able to return to their previous pursuits.
The U.N.’s International Atomic Energy Agency, in information published in 2011, concluding that the Amad project was a coordinated effort to build a nuclear weapon that was shelved in 2003.
In a 2015 report on Iran’s past nuclear activities, the IAEA assessed that while there were some nuclear weapons-related activities after 2003, they didn’t take place in a coordinated fashion.
Mr. Netanyahu, however, said in his presentation Monday that Israel could prove Iran was saving material from the project “to use at a time of its choice to develop nuclear weapons.”
Because Iran has preserved its nuclear documentation and its nuclear experts still reside in the country, Mr. Netanyahu described the nuclear effort as a continuing project.
Mr. Netanyahu gave his presentation hours after missiles hit Syrian bases in Hama and Aleppo, killing more than a dozen Iranian troops, according to the Syrian Observatory for Human Rights. Syrian pro-regime media accused Israel of being behind the attack.
Israeli military declined to comment on the allegations. U.S. officials said neither they nor members of the coalition against Islamic State in Syria initiated the missile strikes.
The presentation touched off a debate among experts and former officials about the value of the new information claimed by Mr. Netanyahu, whether it offered any new information or backed either side of the argument about the Iran nuclear deal.
“Netanyahu is telling us something we already knew—that Iran had a nuclear weapons program,” said Jeffrey Lewis of the James Martin Center for Nonproliferation Studies at the Middlebury Institute of International Studies at Monterey, Calif., in a Twitter message.
However, the materials offered by Mr. Netanyahu deepened mistrust among those critical of the nuclear agreement.
“Anyone who doesn’t think Iran was lying and still is lying doesn’t know Iran,” said Ari Fleischer, who was press secretary to former President George W. Bush.
Iranian Foreign Minister Javad Zarif called Mr. Netanyahu “the boy who can’t stop crying wolf.”
“You can only fool some of the people so many times,” he said.
—Asa Fitch in Dubai and Sune Engel Rasmussen in Beirut contributed to this article.
Write to Felicia Schwartz at Felicia.Schwartz@wsj.com