A series of targets in Iran are in Israel's sights

According to the Times of Israel, Iran's nuclear program is spread across many locations. Although the threat of Israeli airstrikes has existed for decades, only a few nuclear facilities are built underground.

The United States and the United Nations nuclear watchdog believe Iran had a secret nuclear weapons program that it halted in 2003. Iran has denied that such a program exists.

Iran agreed to curb its nuclear activities in exchange for the easing of international sanctions under a 2015 deal with world powers. The pact fell apart after the US withdrew in 2018 and Iran began to waive restrictions the following year.

Since then, Iran has expanded its uranium enrichment program, shortening the so-called breakout time needed to produce enough uranium for a nuclear bomb to within weeks, from at least a year under the 2015 deal.

Here are some of Iran's major nuclear facilities:

Natanz

Natanz, the center of Iran's uranium enrichment program, is a complex located in a mountainous plain outside the city of Qom, south of the capital Tehran. Among the facilities at Natanz are two uranium enrichment plants: the underground fuel enrichment plant (FEP) and the aboveground pilot fuel enrichment plant (PFEP).

In 2002, a group of Iranian exiles revealed that Tehran had secretly built Natanz, causing a diplomatic deadlock between the West and Iran over the country's nuclear intentions.

FEP was built for commercial-scale uranium enrichment, it can accommodate 50,000 centrifuges. About 14,000 centrifuges are installed, of which about 11,000 are operating, refining uranium to a purity of up to 5%.

Diplomats familiar with Natanz describe FEP as being about three stories underground, and there has been debate about how much damage Israeli airstrikes could have caused. In April 2021, Iran said an explosion and power outage at FEP had occurred, which it blamed on an Israeli attack.

Iran's Pilot Fuel Enrichment Plant (PFEP) is above ground, but contains only a few hundred centrifuges. Iran is enriching uranium to 60% purity here.

Fordo

Located on the opposite side of Qom, Fordo is a uranium enrichment facility hidden deep in a mountain and is therefore better protected from airstrikes than FEP. Iran currently has around 1,000 centrifuges at the facility, some of which are advanced IR-6 machines that can enrich uranium to 60%. Iran has recently doubled the number of centrifuges installed at Fordo, all of which are IR-6.

In 2009, the US, UK and France announced that Iran had secretly built the Fordo facility for many years without informing the International Atomic Energy Agency (IAEA). Then US President Barack Obama said: "The scale and structure of this facility are not consistent with a peaceful program."

Isfahan

Iran has a major nuclear technology center on the outskirts of Isfahan, its second-largest city. The center includes the Fuel Plate Fabrication Plant (FPFP) and the Uranium Conversion Facility (UCF) that can process uranium into uranium hexafluoride.

In Isfahan, Iran houses uranium enrichment facilities – a process particularly sensitive to nuclear proliferation, as it can be used to make the core of a nuclear bomb.

Khondab

Iran has a partially built heavy water research reactor called Arak, now renamed Khondab. Heavy water reactors pose a proliferation risk because they can easily produce plutonium, like enriched uranium, which is the core material of an atomic bomb.

Under the 2015 deal between Iran and world powers, construction at Khondab was halted, the reactor core was removed and filled with concrete to render it unusable. The reactor was redesigned “to minimize and not produce weapons-grade plutonium during normal operations.”

Iran has informed the IAEA of plans to put the reactor into operation by 2026.

Bushehr

Iran's only operating nuclear power plant uses Russian fuel, which Russia then takes back when it is finished, helping to reduce proliferation risks.