A new U.S. intelligence report found that Iran's nuclear program has been set back by only a few months after a U.S. strike, and was not "completely and fully obliterated" as U.S. President Donald Trump has said, according to two people familiar with the early assessment.

The early intelligence report issued by the U.S. Defence Intelligence Agency (DIA) on Monday contradicts statements from Trump and Israeli Prime Minister Benjamin Netanyahu about the status of Iran's nuclear facilities. The people were not authorized to address the matter publicly and spoke on condition of anonymity.

According to the people, the report found that while the Saturday strikes at the Fordow, Natanz and Isfahan nuclear sites did significant damage, the sites were not totally destroyed.

The assessment found that at least some of Iran's highly enriched uranium was moved out of multiple sites before the strikes and survived, according to the people. It also found that Iran's centrifuges are largely intact.

At the deeply buried Fordow uranium enrichment plant, the entrance collapsed but the underground infrastructure was not destroyed, according to one of the people. The person also said that previous assessments had warned of this outcome at Fordow.

White House pushes back

The White House strongly pushed back on the assessment, calling it "flat-out wrong."

"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," White House press secretary Karoline Leavitt said in a statement. "Everyone knows what happens when you drop 14 30,000-pound bombs perfectly on their targets: total obliteration."

WATCH | NATO chief reaches out to Trump: 

NATO secretary general compliments Trump after U.S. strike on Iran nuclear site sites

U.S. President Donald Trump posted a screenshot of a message sent to him from NATO Secretary General Mark Rutte on social media Tuesday. In the text exchange, Rutte congratulated him for his 'decisive action' in Iran and getting all NATO allies to agree to spend at least five per cent of their GDP on defence.

Trump has said in comments and posts on social media in recent days, including Tuesday, that the strikes "totally destroyed" the sites and that Iran will never rebuild its nuclear facilities.

The U.S. president has said the attacks were necessary to prevent Iran from developing a nuclear weapon. Iran denies it is seeking such a weapon and says its nuclear program is for peaceful purposes.

Netanyahu applauds 'historic' U.S. involvement

Netanyahu said in a televised statement on Tuesday that, "For dozens of years I promised you that Iran would not have nuclear weapons and indeed ... we brought to ruin Iran's nuclear program."

He said the U.S. joining Israel was "historic" and thanked Trump.

The U.S. Central Intelligence Agency and Office of the Director of National Intelligence (ODNI) declined to comment on the DIA assessment. ODNI co-ordinates the work of the nation's 18 intelligence agencies, including the DIA, which is the intelligence arm of the U.S. Defence Department, responsible for producing intelligence on foreign militaries and the capabilities of adversaries.

The intelligence assessment was first reported by CNN on Tuesday. Reuters and the New York Times also published reports on the DIA assessment.

Democrats have previously said Trump's claims that the weekend strikes eliminated or seriously set back Iran's nuclear program were not yet backed by evidence.

"There's zero evidence that I've seen that the nuclear program was completely and totally obliterated, as Donald Trump has claimed," U.S. House of Representatives Democratic Leader Hakeem Jeffries said on Monday.

Classified briefings on the matter for members of the House of Representatives and U.S. Senate were cancelled on Tuesday.

William Hague, a former U.K. foreign secretary, said regardless of how much damage was done by the U.S. strikes, it will still be an ongoing challenge to prevent Iran from developing a nuclear weapon.

"In the long run, it's going to be very hard to stop nuclear weapons proliferating by using force," Hague told Times Radio. "That is going to need agreements.

"And a humiliated and defeated power in history normally finds a way of coming back again — in this case, with a nuclear weapon — in the future."