President Donald Trump said on Saturday the U.S. military had conducted a "very successful attack" on nuclear sites in Iran, including a facility buried deep in a mountain at Fordo, south of Tehran.

Israel has hit Iranian nuclear sites since launching attacks on Iran on June 13, including striking Natanz, which is at the heart of Iran's uranium enrichment program, and Khondab, a partially built heavy-water research reactor.

Below are some of Iran's main nuclear facilities.

Where Are Iran's Nuclear Facilities?

Iran's nuclear program is spread over many locations. While the threat of Israeli airstrikes has loomed for decades, only some of the sites have been built underground.

Does Iran Have a Nuclear Weapons Program?

The United States and the U.N. nuclear watchdog believe Iran had a coordinated, secret nuclear weapons program that it halted in 2003. The Islamic Republic denies ever having had one or planning to have one.

Iran agreed to restrictions on its nuclear activities in exchange for relief from international sanctions under a 2015 deal with world powers. That pact fell apart after Trump, in his first term as president, pulled the United States out of it in 2018. Tehran started abandoning the restrictions in the following year.

Is Iran Increasing Its Uranium Enrichment?

Yes. Iran has been expanding its uranium enrichment program since the pact broke down, reducing the "breakout time" needed to produce enough weapons-grade uranium for a nuclear bomb to days or little more than a week from at least a year under the 2015 deal.

Actually making a bomb with that material would take longer. How long is less clear and is the subject of debate.

Iran is now enriching uranium to up to 60% fissile purity, close to the 90% of weapons-grade, at two sites, and in theory it has enough material enriched to that level, if enriched further, for six bombs, according to a yardstick of the International Atomic Energy Agency, the U.N. watchdog.

Natanz

A complex at the heart of Iran's enrichment program on a plain abutting mountains outside the Shi'ite Muslim holy city of Qom, south of Tehran. Natanz houses facilities including two enrichment plants: the vast, underground Fuel Enrichment Plant and the aboveground Pilot Fuel Enrichment Plant.

An exiled Iranian opposition group revealed in 2002 that Iran was secretly building Natanz, igniting a diplomatic standoff between the West and Iran over its nuclear intentions that continues today.

The FEP was built for enrichment on a commercial scale, able to house 50,000 centrifuges. Before the Israeli and U.S. attacks, around 16,000 centrifuges were installed there, roughly 13,000 of them in operation, refining uranium to up to 5% purity.

Diplomats with knowledge of Natanz describe the FEP as being about three floors belowground. There has long been debate about how much damage Israeli airstrikes could do to it.

Damage has been done to centrifuges at the FEP by other means, including an explosion and power cut in April 2021 that Iran said was an attack by Israel.

The aboveground PFEP houses only hundreds of centrifuges but Iran has been enriching to up to 60% purity there.

Fordo

On the opposite side of Qom, Fordo is an enrichment site dug into a mountain and, therefore, probably better protected from potential bombardment than the FEP. Trump posted on social media after the U.S. strikes: "Fordow is gone."

The 2015 deal with major powers did not allow Iran to enrich at Fordo at all. Before the Israeli and U.S. attacks, the facility had around 2,000 centrifuges operating, most of them advanced IR-6 machines, of which up to 350 were enriching to up to 60%.

The United States, Britain, and France announced in 2009 that Iran had been secretly building Fordo for years and had failed to inform the IAEA. Then-President Barack Obama said then: "The size and configuration of this facility is inconsistent with a peaceful program."

Isfahan

Iran has a large nuclear technology center on the outskirts of Isfahan, its second largest city.

It includes the Fuel Plate Fabrication Plant and the uranium conversion facility that can process uranium into the uranium hexafluoride that is fed into centrifuges.

Iran also stores enriched uranium at Isfahan, diplomats say.

There is equipment at Isfahan to make uranium metal, a process that is particularly proliferation-sensitive since it can be used to devise the core of a nuclear bomb.

The IAEA has said there are machines for making centrifuge parts at Isfahan, describing it in 2022 as a "new location."

Khondab

Iran has a partially built heavy-water research reactor, originally called Arak and now Khondab. Heavy-water reactors pose a nuclear proliferation risk because they can easily produce plutonium which, like enriched uranium, can be used to make the core of an atomic bomb.

Under the 2015 deal, construction was halted and the reactor's core was removed and filled with concrete to make it unusable. The reactor was to be redesigned "to minimize the production of plutonium and not to produce weapon-grade plutonium in normal operation." Iran informed the IAEA that it planned to start operating the reactor in 2026.

Tehran Research Center

Iran's nuclear research facilities in Tehran include a research reactor.

Bushehr

Iran's only operating nuclear power plant, on the Gulf coast, uses Russian fuel that Russia then takes back when it is spent, reducing the proliferation risk.