The U.S. strike on Iran's Fordow nuclear site sent bombs directly down exposed vent shafts after blowing off concrete covers, according to Defense Secretary Pete Hegseth.

Hegseth "says the photos showing the groups of 3 holes in the ground at the Iranian Fordow nuclear facility are actually exposed ventilation shafts after U.S. bombs blew off concrete caps Iranians placed, then U.S. bombs went down the center exposed vent holes," Fox News's Bill Melugin wrote Thursday morning on X.

The revelation comes as U.S. and Israeli officials have said that the U.S. strike dealt a crippling blow to Iran's nuclear program. Israel's Atomic Energy Commission assessed the Fordow site as "inoperable" and said the strike "set back Iran's ability to develop nuclear weapons by many years." A CIA report supported that view, with Director John Radcliffe saying Iran's nuclear program is "severely damaged," setting back the Islamic Republic's ambitions by years.

President Donald Trump said Wednesday that Iran no longer has a nuclear program and warned that any attempt to restart it would trigger more U.S. attacks.

American forces on Saturday used seven B‑2 stealth bombers to drop 14 "bunker-buster" bombs and launched at least 30 Tomahawk cruise missiles against Iran's Esfahan and Natanz nuclear sites, according to reports.

Joint Chiefs of Staff chairman Gen. Dan Caine said Thursday morning that the United States spent 15 years developing the heavy-duty bunker busters, starting the program in 2009 after learning about Iran's construction of the Fordow nuclear facility, CBS News's Jennifer Jacobs reported.

Pentagon officials "knew from the very first days what [the facility] was for—you do not build a multi-layered underground bunker complex with centrifuges and other equipment in a mountain for any peaceful purpose," Caine said.