Bombing Iranian nuke plant with US bunker-buster bomb might not work: Expert

An attack on a key Iranian nuclear facility might not be effective, even if the U.S. military's massive bunker-buster bombs are used, a national security expert familiar with Iran's program said.

While the 30,000-pound bombs have been tested, they've never actually been used and the exact nature of the concrete and metal protecting the site located deep inside a mountain -- that the bombs would need to penetrate -- isn't fully known.

Joe Cirincione, who has spent decades researching nuclear proliferation for Congress and other world leaders, told ABC News that while attacking Iran's nuclear enrichment program would cripple its nuclear weapons capability, it would not eliminate it.

At the center of President Donald Trump's decision on whether to attack Iran is the Fordo nuclear enrichment facility in northwest Iran. It's said to be built 300 feet deep inside a mountain -- maybe more -- and reinforced with concrete, according to experts.

The U.S. weapon touted as able to strike inside the Fordo facility the GBU-57 A/B Massive Ordnance Penetrator bomb, known as a "bunker buster." It's capable of penetrating 200 feet deep inside an underground target and then exploding, experts say.