AP Explains: Iran's nuclear facility deep inside a mountain

DUBAI, United Arab Emirates (AP) — Iran's Fordo nuclear facility sits deep inside a mountain, with just one structure visible from space.

Western intelligence officials have worried about the site since 2008, when satellite images caught work at the site just outside of the Shiite holy city of Qom, some 120 kilometers (75 miles) southwest of Iran's capital, Tehran.

Israel and the U.S. worried that the size of the facility, its hardened position and its air defenses signaled that it could be used for military activities — such as potentially enriching uranium for a nuclear weapon.

Iran long has insisted its program is for peaceful purposes, but the facility came to light amid a major Western pressure campaign over Tehran's atomic program under hard-line Iranian President Mahmoud Ahmadinejad.

As Israel threatened at one point to bomb Iranian nuclear sites like Fordo, U.S. officials showed them a video of a bunker-buster bomb destroying a mock-up of Fordo in America's southwestern desert, The New York Times reported in September.

The 2015 nuclear deal between Tehran and world powers saw it give up enrichment at the site.

However, Iran's President Hassan Rouhani announced Tuesday that his government will start injecting uranium gas into over a thousand centrifuges at Fordo.

It's Tehran's latest step away from the nuclear deal, which has been collapsing since President Donald Trump withdrew from the agreement over a year ago.