The spokesperson, Sean Parnell, repeated Donald Trump’s claim that Iran’s key nuclear sites had been completely destroyed, although he did not offer further details on the origin of the assessments beyond saying it came from inside the defense department.

“We have degraded their program by one to two years,” Parnell said at a news conference held at the Pentagon.

“At least, intel assessments inside the department assess that.”

Parnell’s description of the strikes marked a more measured estimate than Trump’s assertions about the level of destruction. A low-confidence Defense Intelligence Agency (DIA) report based on early assessments said Iran’s program was set back several months.

The evolving picture of the severity of the damage to Iran’s nuclear program comes as US intelligence agencies have continued to push out new assessments, using materials that suggested the centrifuges at the key Fordow enrichment site were destroyed even if it was unclear whether the facility itself had caved in.

Trump advisers have used that material, which include the use of video taken from B-2 bombers to confirm simulation models of shock waves destroying centrifuges and other Israeli intel from outside Fordow, to defend Trump’s assertions, two people familiar with the matter stated.

The extent of the damage to Iran’s nuclear program and the fate of the country’s stockpile of enriched uranium – which could quickly be turned into a crude nuclear weapon – is important because it could dictate how long the program has been set back.

The head of the UN nuclear watchdog noted on Sunday that Iran could be producing enriched uranium in a few months.

“They can have in a matter of months, I would say, a few cascades of centrifuges spinning and producing enriched uranium,” Rafael Grossi the head of the International Atomic Energy Agency (IAEA) stated, adding “Iran is a very sophisticated country in terms of nuclear technology … You cannot undo the knowledge that you have or the capacities that you have.”

The Pentagon’s preliminary DIA assessment, which was based on information from little more than 24 hours after the strikes found the damage could range from Iran being able to restart the facility with new centrifuges to having to abandon it for future use.

The DIA report assessed the program had been pushed back by several months, although that finding was made at the so-called “low-confidence” level, reflecting the early nature of the assessment and the uncertainty intelligence agencies have with initial conclusions.

Trump advisers have pushed back on the DIA report and said privately the destruction of the centrifuges alone meant they had taken out a key component of Iran’s ability to develop nuclear weapons and meant it delayed the nuclear program by years.

Battles over the conclusions of intelligence agencies have been at the center of American foreign policy determinations for decades, from warnings about Iraq’s weapons programs that the Bush administration used to justify the 2003 invasion that were later found to be false, to claims that a Chinese lab leak was responsible for Covid.

Still, much of the controversy about the US strikes has been generated by Trump’s claiming that they “obliterated” Iran’s nuclear sites, which no intelligence agency has directly repeated because it is not a characterization used in intelligence assessments.

Verifying the extent of the damage was made more difficult on Wednesday, after Iran put into effect a new law to suspend cooperation with the IAEA. Iran has accused the nuclear watchdog of siding with western countries and providing a justification for Israel’s airstrikes.

A state department spokesperson called the move “unacceptable” and added Iran must fully comply with its nuclear non-proliferation treaty obligations, including by providing the IAEA with information on undeclared nuclear material and providing unrestricted access to any newly announced enrichment facility.