The Pentagon said on Wednesday that U.S. strikes had degraded Iran's nuclear program by up to two years after destroying the three targeted sites.

Sean Parnell, a Pentagon spokesman, offered the estimate at a briefing to reporters, adding that the official estimate was "probably closer to two years."

U.S. military bombers carried out strikes against three Iranian nuclear facilities on June 22 using more than a dozen 30,000-pound (13,600-kg) bunker-buster bombs.

The results of the strikes are being closely watched to see how far they may have set back Iran's nuclear program, after President Donald Trump said it had been obliterated.

Over the weekend, the head of the U.N. nuclear watchdog Rafael Grossi said that Iran could be producing enriched uranium in a few months, raising doubts about how effective U.S. strikes to destroy Tehran's nuclear program have been.