TEL AVIV/WASHINGTON (Reuters) - Israeli Prime Minister Benjamin Netanyahu unveiled on Monday what he said was evidence of a secret Iranian nuclear weapons program that could step up pressure on the United States to pull out of a 2015 nuclear deal with Iran.

U.S. Secretary of State Mike Pompeo said the information showed that Iran’s leaders lied to their people about a nuclear weapons program known as “Project Amad”. But Pompeo declined to say whether the documents provided evidence of a violation of the nuclear deal.

Intelligence experts and diplomats said Netanyahu’s presentation, in a prime-time television presentation, did not seem to have a “smoking gun” showing a violation by Iran but it could strengthen the hand of advisers to U.S. President Donald Trump who want to scrap the nuclear agreement.

Most of the purported evidence Netanyahu presented dated to the period before the 2015 accord was signed, although he said Iran had also kept important files on nuclear technology since then, and continued adding to its “nuclear weapons knowledge”.

Tehran dismissed Netanyahu as “the boy who cried wolf”, and called his presentation propaganda.

As he traveled back from Amman, Jordan, to Washington on Monday, Pompeo told reporters he and Netanyahu discussed the documents in Tel Aviv during a meeting on Sunday.

Pompeo said that while the existence of the Amad nuclear project was known for some time, the new material discovered by the Israelis will help better understand the scope and scale of the program.

He added that the documents make “very clear that at the very least the Iranians have continued to lie to their own people.”

Asked whether the information indicated a violation of the Iran nuclear agreement, Pompeo responded: “I‘ll leave that to lawyers. The president will ultimately have to make a determination about that too.”

Trump has threatened to pull the United States out of the international deal unless it is renegotiated by May 12. After Netanyahu spoke, Trump repeated his criticism of the deal, suggesting he backed the Israeli leader’s remarks.

At Israel’s Defence Ministry, Netanyahu stood in front of stacks of files representing what he described as a vault full of Iranian nuclear documents obtained weeks before.

“Iran lied about never having a nuclear weapons program,” he said. “One hundred thousand secret files prove it did. Second, even after the deal, Iran continued to preserve and expand its nuclear weapons knowledge for future use.”

Although the presentation was live on Israeli television, Netanyahu made clear his audience was abroad, delivering most of his speech in English, before switching to Hebrew.

Netanyahu said he had shared the intelligence with the United States and would dispatch envoys to France and Germany to present it. He also spoke by phone to Russian President Vladimir Putin.

The White House later acknowledged receiving the information from Israel, saying it was examining it carefully.

“This information provides new and compelling details about Iran’s efforts to develop missile-deliverable nuclear weapons. These facts are consistent with what the United States has long known: Iran had a robust, clandestine nuclear weapons program that it has tried and failed to hide from the world and from its own people,” the White House said in a statement.

An earlier statement by the White House stated that Iran “has” a clandestine nuclear weapons program before it corrected it to due to what it said was a clerical error.

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A 2007 National Intelligence Estimate judged with “high confidence” that Tehran halted its nuclear weapons program in the fall of 2003. The IAEA later reached a similar judgment.

Iran has denied ever seeking nuclear weapons and accuses its arch-foe Israel of stirring up world suspicions against it.

A White House official said the information provided compelling details about “Iran’s past efforts” to develop nuclear weapons.

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ANALYSTS, DIPLOMATS SKEPTICAL

Under the 2015 nuclear deal struck by Iran and six major powers - Britain, China, France, Germany, Russia and the United States - Tehran agreed to limit its nuclear program in return for relief from U.S. and other economic sanctions.

Trump gave Britain, France and Germany a May 12 deadline to fix what he views as the deal’s flaws - its failure to address Iran’s ballistic missile program, the terms by which inspectors visit suspect Iranian sites, and “sunset” clauses under which some of its terms expire - or he will reimpose U.S. sanctions.

Much of what Netanyahu presented is unlikely to surprise world powers, which have long concluded that Iran was pursuing atomic weapons before the agreement was signed in 2015. That is in part why they imposed sanctions in the first place.

The French ambassador to Washington, Gerard Araud, tweeted that information about past Iranian nuclear activity was in fact an argument in favor of the nuclear deal, not against it.

A German government spokesman said it was vital to keep the independent inspections provided for under the deal.

Some independent analysts and diplomats said Netanyahu appeared to be presenting old evidence.

A British government spokesman defended the accord, saying in a statement: “We have never been naive about Iran and its nuclear intentions.”

“That is why the IAEA inspection regime agreed as part of the Iran nuclear deal is one of the most extensive and robust in the history of international nuclear accords,” the spokesman added.

Speaking after Netanyahu’s presentation, Trump told a White House news conference the nuclear deal was “a horrible agreement for the United States”. He said it would let Tehran develop nuclear arms after seven years and had “proven right what Israel has done today” with Netanyahu’s disclosures.

Washington itself has concluded, however, that Iran has not violated the deal’s terms. Two U.S. intelligence officials who have monitored Iran’s nuclear weapons program for years said nothing in Netanyahu’s remarks appeared to contradict that view.

“We have seen no new and credible evidence that Iran is violating the agreement, whether in the Prime Minister’s remarks today or from other sources,” said one of the officials, both of whom spoke on the condition of anonymity.

Moments before Netanyahu spoke Iranian Foreign Minister Mohammad Javad Zarif tweeted: “The boy who can’t stop crying wolf is at it again”.

Israel is widely believed to be the only nuclear-armed state in the Middle East, although it neither confirms nor denies possessing atomic weapons.