Pompeo met Israel's Prime Minister Benjamin Netanyahu on Sunday at Israeli military headquarters and was briefed on the material, which was released as Washington's new top diplomat flew home.

"We've known about this material for a while and we certainly discussed this material yesterday when we were together," Pompeo told reporters on his plane.

"It's been something that's been in the works for a while. I know that there are people talking about these documents not being authentic. I can confirm with you, for you, that these documents are real, they are authentic."

Asked whether the United States had been aware for many years that Iran had a secret nuclear weapons program -- dubbed Project Amad -- before 2004, Pompeo said: "That's partly true. The existence of the Amad program ended roughly in December 2003, January 2004.

"It's accurate to say that the knowledge of that, the fact of that, has been known for quite some time, but there are thousands of new documents and new information," the top US diplomat added.

"We're still going through it, there's still a lot of work to do to figure out the scope and scale of it, but it is the case that there is new information about that program."

Supporters of the 2015 Iran nuclear deal, which President Donald Trump is expected to pull the US out from on May 12, have argued that Netanyahu's intelligence release deals simply with a historic Iranian program and does not prove they are in breach of the 2015 accord.

But Pompeo argued that it has some value in the current debate.

"This will, I think, spell out the scope and scale of the program that they undertook there, and I think that it makes clear that at the very least the Iranians have continued to lie to their own people," he told reporters.

"The Iranians have consistently taken the position that they've never had a program like this. This will belie any notion that there wasn't a program."

Pompeo said that Trump would have to determine whether the United States feels Iran is in violation of the deal, and said US translators and analysts are still trawling through the intelligence provided by the Israelis.