American B-2 bombers hit two Iranian nuclear sites with massive GBU-57 bunker-buster bombs last weekend, while a guided missile submarine struck a third site with Tomahawk cruise missiles.

President Donald Trump "created the conditions to end the war, decimating -- choose your word -- obliterating, destroying Iran's nuclear capabilities," Defense Secretary Pete Hegseth said during a news conference at the Pentagon, referring to a 12-day conflict between Israel and Iran.

Trump himself has called the strikes a "spectacular military success" and repeatedly said they "obliterated" the nuclear sites.

But US media revealed a preliminary American intelligence assessment earlier this week that said the strikes only set back Iran's nuclear program by months -- coverage sharply criticized by Hegseth and others.

"Whether it's fake news CNN, MSNBC or the New York Times, there's been fawning coverage of a preliminary assessment," Hegseth said.

The document was "leaked because someone had an agenda to try to muddy the waters and make it look like this historic strike wasn't successful," he said.

Trump -- who has also personally slammed coverage of the intelligence report, calling for journalists to lose their jobs -- on Thursday accused Democrats of leaking the assessment and said they should be prosecuted.

- 'Get a big shovel' -

White House Press Secretary Karoline Leavitt meanwhile told journalists that the Iran strikes were "one of the most successful operations in United States history," and joined Trump in lashing out personally at CNN's Natasha Bertrand -- one of the reporters who broke the story on the preliminary assessment.

Bertrand has been "used by people who dislike Donald Trump in this government to push fake and false narratives," Leavitt said.

CNN has issued a statement saying it stands behind the journalist and her reporting.

In his remarks Thursday morning, Hegseth did not definitively state that the enriched uranium and centrifuges at the heart of Iran's controversial nuclear program had been wiped out. He cited intelligence officials as saying the nuclear facilities were destroyed, but gave little detail.

"If you want to know what's going on at Fordo, you better go there and get a big shovel, because no one's under there right now," he said, referring to the deep-underground nuclear site.

Among the officials cited by Hegseth was US Director of National Intelligence Tulsi Gabbard, who said the previous day that "Iran's nuclear facilities have been destroyed."

He also referred to a statement by CIA chief John Ratcliffe, who pointed to a "historically reliable and accurate" source of information indicating that "several key Iranian nuclear facilities were destroyed and would have to be rebuilt over the course of years."

Israel launched an unprecedented air campaign targeting Iranian nuclear sites, scientists and top military brass on June 13 in a bid to end the country's nuclear program, which Tehran says is for civilian purposes but Washington and other powers insist is aimed at acquiring atomic weapons.

Trump had spent weeks pursuing a diplomatic path to replace the nuclear deal with Tehran that he tore up during his first term in 2018, but he ultimately decided to take military action.

The US operation was massive, involving more than 125 US aircraft including stealth bombers, fighters and aerial refueling tankers as well as a guided missile submarine.