The head of the United Nations’ nuclear watchdog has obliterated President Donald Trump’s claims about the efficacy of the United States’ strikes on Iran.

Rafael Grossi said American B-2 bombers did not cause total damage—or “completely and totally obliterate,” as Trump said—to the Iranian nuclear program. Instead, he estimates Tehran can restart enriching uranium again “in a matter of months.”

Rafael Grossi, 64, said there was not “total damage” at Iranian nuclear sites, as President Donald Trump claims. Elisabeth Mandl/REUTERS

Grossi’s remarks are a blow to Trump and his administration, which has dismissed a leaked attack assessment from U.S. intelligence—which reached a similar conclusion as Rossi—as incomplete and untrue since CNN first reported on it Wednesday.

“The capacities they have are there,” Grossi told CBS News’ Face The Nation about Iran’s nuclear program. “They can have, you know, in a matter of months, I would say, a few cascades of centrifuges spinning and producing enriched uranium, or less than that. But as I said, frankly speaking, one cannot claim that everything has disappeared and there is nothing there.”

Donald Trump has claimed the U.S. attack on Iran set the Iranian nuclear program back years despite intelligence from the Pentagon estimating it was only pushed back months. White House/via Reuters

Grossi, 64, is the director general of the International Atomic Energy Agency—the agency that conducts inspections at nuclear sites around the world. He noted that the U.S. military had “severely damaged” a trio of Iranian nuclear sites. Still, he said there is no indication that the program has been set back years, as the White House and Pentagon claim.

“It is clear that there has been severe damage, but it’s not total damage,” he said.

The Argentine added of Iran, “If they so wish, they will be able to start doing this again.”

The U.S. attack on Iran’s nuclear facilities was carried out by piloted B-2 bombers that flew round-trip from Missouri. U.S. Air National Guard/Master Sgt. Patrick Evenson/Handout via

A hotly contested debate has erupted over whether Iran was able to remove enriched uranium from its facilities ahead of the U.S. dropping bunker buster bombs. Trump says Iran was not able to, while Tehran insists that it did.

Grossi said it is not clear. He noted that Iran said it was taking protective measures ahead of the strike, which would logically include moving uranium—its most crucial material—from nuclear sites, assuming they were able to.

Fordow, one of three Iranian nuclear sites struck by U.S. bombs this month, was built in 2006 but remained secret until foreign intelligence services uncovered it by 2009. Eric Faison/The Daily Beast

The director made clear his goal was not to undercut Trump. He pushed for a diplomatic solution with Iran, pointing out that the country has not always been truthful with U.N. inspectors over its potential progress toward a nuclear weapon. He said his watchdog group has found traces of uranium in Iran outside its three known nuclear enrichment sites.

“We were asking for years, ‘Why did we find these traces of enriched uranium in place x, y, or z?’” he said. “And we were simply not getting credible answers.”

Inspectors have been shut out of Iran entirely since Israel attacked it on June 13, Grossi said. He pushed the country to let the U.N. in again.

Grossi also noted that prior checks in Iran did not reveal proof that it was nearing the completion of a nuclear weapon—a conclusion also reached by United States Director of National Intelligence Tulsi Gabbard earlier this year. Gabbard has since changed her tune to say that Iran was indeed months away from producing a nuclear bomb after Trump called her assessment “wrong.”

Iran Supreme Leader Ali Khamenei said on Iranian state television that the U.S. had not decimated its nuclear sites, as President Donald Trump and other White House officials have claimed. Office of the Iranian Supreme Le/via REUTERS

Grossi said Iran’s secrecy made it hard to be certain.