US President Donald Trump has labelled an intelligence report into the damage done to the Iranian nuclear programme as "inconclusive".
However, he suggested that the damage could have been "severe".
"The intelligence was very inconclusive. The intelligence says we don't know. It could've been very severe. That's what the intelligence suggests," Mr Trump told reporters ahead of attending the NATO summit.
"It was very severe. There was obliteration," he added.
When asked if the United States would strike again if Iran rebuilt its nuclear enrichment programme, Mr Trump said: "Sure."
Earlier, Mr Trump rebuffed US media reports of intel that found that the US strikes on Iran set back the nation's nuclear programme by a few months.
This was after he stated on social media that the nuclear sites had been "completely destroyed".
Israeli Prime Minister Benjamin Netanyahu has declared a "historic victory" against Iran despite the US intelligence report.
Iran and Israel agreed a ceasefire yesterday ending 12 days of tit-for-tat strikes, after Mr Trump joined the conflict with bunker-busting bombs at the weekend that he said destroyed key Iranian nuclear sites.
Watch: Donald Trump says damage from US strikes on Iran caused 'severe' damage
White House Press Secretary Karoline Leavitt confirmed the authenticity of the US intel, but said it was "flat-out wrong".
In an address to the nation after the ceasefire announcement, Mr Netanyahu said: "Iran will not have a nuclear weapon".
"We have thwarted Iran's nuclear project," he said. "And if anyone in Iran tries to rebuild it, we will act with the same determination, with the same intensity, to foil any attempt."
UN agency to inspect Iranian nuclear sites
The head of the UN nuclear agency Rafael Grossi said his inspectors' top priority is returning to Iran's nuclear facilities to assess the impact of recent military strikes on Tehran's nuclear programme.
"This is the number one priority," Mr Grossi said, speaking to reporters at an Austrian cabinet meeting in Vienna.
He is seeking his inspectors' return to Iranian sites, including the three plants where it was enriching uranium until Israel launched strikes on 13 June.
Asked if Iran had informed him of the status of its stocks of enriched uranium, particularly its uranium enriched to up to 60% purity, close to weapons grade, he pointed to a letter he received from Iran.
He said Iran would take "special measures" to protect its nuclear materials and equipment.
"They did not get into details as to what that meant but clearly that was the implicit meaning of that. We can imagine this material is there," Mr Grossi said, suggesting much of that material had survived the attacks.
Iran's parliament approved a bill to suspend cooperation with the IAEA, state-affiliated news outlet Nournews reported, adding that such a move would require approval of the top security body.
Cooperating with the IAEA is a requirement under the non-proliferation treaty that gives Iran access to nuclear technology as long as it refrains from pursuing a weapon.
Israel had said its bombing campaign was aimed at preventing Iran from acquiring a nuclear weapon, an ambition Iran has consistently denied.
Israel's military said that its strikes had set back Iran's nuclear programme "by years".
After Mr Trump angrily berated both sides for early violations of the truce, Iran announced it would respect the terms of the deal if Israel did the same, while Israel said it had refrained from further strikes.
Iranian President Masoud Pezeshkian said his country was willing to return to negotiations over its nuclear programme, but that his country would continue to "assert its legitimate rights" to the peaceful use of atomic energy.
Leaked US intel
US media cited people familiar with the Defense Intelligence Agency findings as saying the US strikes did not fully eliminate Iran's centrifuges or stockpile of enriched uranium.
The strikes sealed off entrances to some facilities without destroying underground buildings, according to the report.
Ms Leavitt responded on social media: "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 programme."
While Iran and Israel have been locked in a shadow war for decades, their 12-day conflict was by far the most destructive confrontation between them.
Israeli strikes hit nuclear and military targets - killing scientists and senior military figures - as well as residential areas, prompting waves of Iranian missile fire on Israel.
Watch: JD Vance hails US President's decision to strike Iranian nuclear sites
The war culminated in US strikes on underground Iranian nuclear sites using bunker-busting bombs - which Israel lacks - followed by an Iranian reprisal targeting the largest US military facility in the Middle East, based in Qatar.
Mr Trump shrugged off that response as "weak", thanking Iran for giving advance notice and announcing the contours of the ceasefire just hours later.
