Iran could resume producing enriched uranium within months, U.N. nuclear watchdog chief Rafael Grossi warned Sunday, casting doubt on the effectiveness of recent U.S. strikes aimed at crippling Tehran’s nuclear program.

U.S. officials have stated that their strikes obliterated key nuclear sites in Iran, although U.S. President Donald Trump said Friday he would consider bombing Iran again if Tehran is enriching uranium to worrisome levels.

"The capacities they have are there. 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," Grossi told CBS News in an interview.

"Frankly speaking, one cannot claim that everything has disappeared and there is nothing there," he added, according to the transcript of an interview on "Face the Nation" with Margaret Brennan due to air Sunday.

Saying it wanted to remove any chance of Tehran developing nuclear weapons, Israel launched attacks on Iran earlier this month, igniting a 12-day air war that the U.S. eventually joined.

Iran says its nuclear program is for peaceful purposes only.

Grossi, who heads the Vienna-based International Atomic Energy Agency, said the strikes on sites in Fordo, Natanz and Isfahan had significantly set back Iran's ability to convert and enrich uranium.

However, Western powers stress that Iran's nuclear advances provide it with an irreversible knowledge gain, suggesting that while losing experts or facilities may slow progress, the advances are permanent.

"Iran is a very sophisticated country in terms of nuclear technology," Grossi said. "So you cannot disinvent this. You cannot undo the knowledge that you have or the capacities that you have."

Grossi was also asked about reports of Iran moving its stock of highly enriched uranium in the run-up to the U.S. strikes and said it was not clear where that material was.

"So some could have been destroyed as part of the attack, but some could have been moved," he said.