U.S. missile strikes did not completely destroy Iran's key nuclear sites, an initial American assessment from the Defense Intelligence Agency found, according to three people familiar with the report who spoke to NBC News.

"We were assuming that the damage was going to be much more significant than this assessment is finding," one of the three sources told NBC News. "This assessment is already finding that these core pieces are still intact. That's a bad sign for the overall program."

The assessment also found that the U.S. strikes set Iran's nuclear program back by around three to six months. But Iran's stockpile of enriched uranium was not destroyed and Tehran's centrifuges remain largely intact.

CNN first reported the existence of the report.

The assessment was based on U.S. Central Command's analysis of battle damage from the bombings of three Iranian nuclear facilities over the weekend. That analysis is ongoing.

The New York Times reported that the preliminary, classified report found the bombings did not collapse underground buildings of the Iranian nuclear sites.

The intelligence findings appear to contradict both Trump and Defense Secretary Pete Hegseth, who have asserted that the strikes completely "obliterated" the Iranian nuclear sites.

Asked for comment by CNBC, the Pentagon shared a statement from Hegseth that, "Based on everything we have seen and I've seen it all our bombing campaign obliterated Iran's ability to create nuclear weapons."

"Our massive bombs hit exactly the right spot at each target and worked perfectly," Hegseth said in the statement. "The impact of those bombs is buried under a mountain of rubble in Iran; so anyone who says the bombs were not devastating is just trying to undermine the President and the successful mission."

Trump wrote on Truth Social on Monday, "The sites that we hit in Iran were totally destroyed, and everyone knows it."

White House press secretary Karoline Leavitt told NBC News in a statement that the "alleged assessment is flat-out wrong and was classified as ‘top secret' but was still leaked to CNN by an anonymous, low-level loser in the intelligence community."

"The leaking of this alleged assessment is a clear attempt to demean President Trump, and discredit the brave fighter pilots who conducted a perfectly executed mission to obliterate Iran's nuclear program," Leavitt said.

She added: "Everyone knows what happens when you drop fourteen 30,000 pound bombs perfectly on their targets: total obliteration."

Source: CNBC