What to know about Iran’s nuclear sites

DUBAI, United Arab Emirates (AP) - Israel attacked multiple Iranian nuclear and military sites on Friday as tensions reached new heights over Tehran's rapidly advancing nuclear program.

Israeli leaders said the attack was necessary to head off what they claimed was an imminent threat that Iran would build nuclear bombs. Iran long has insisted its program is peaceful and U.S. intelligence agencies have assessed that Tehran was not actively pursuing the bomb.

The attack came one day after the International Atomic Energy Agency’s Board of Governors censured Iran for the first time in 20 years for not working with its inspectors. Iran immediately announced it would establish a third enrichment site in the country and swap out some centrifuges for more-advanced ones.

The U.S. and Iran had been in talks that could have resulted in the U.S. lifting some of its crushing economic sanctions on Iran in exchange for Tehran drastically limiting or ending its enrichment of uranium.

Here's a look at some major Iranian sites and their importance in Tehran's program.

Iran's nuclear facility at Natanz, located some 220 kilometers (135 miles) southeast of Tehran, is the country's main enrichment site.

Part of the facility on Iran's Central Plateau is underground to defend against potential airstrikes. It operates multiple cascades, or groups of centrifuges working together to more quickly enrich uranium.

Iran also is burrowing into the Kūh-e Kolang Gaz Lā, or Pickax Mountain, which is just beyond Natanz's southern fencing. Natanz has been targeted by the Stuxnet virus, believed to be an Israeli and American creation, which destroyed Iranian centrifuges. Two separate sabotage attacks, attributed to Israel, also have struck the facility.

Iran's nuclear facility at Fordo is located some 100 kilometers (60 miles) southwest of Tehran. It also hosts centrifuge cascades, but isn't as big a facility as Natanz.

Buried under a mountain and protected by anti-aircraft batteries, Fordo appears designed to withstand airstrikes.

Its construction began at least in 2007, according to the International Atomic Energy Agency, although Iran only informed the U.N. nuclear watchdog about the facility in 2009 after the U.S. and allied Western intelligence agencies became aware of its existence.

Iran's only commercial nuclear power plant is in Bushehr on the Persian Gulf, some 750 kilometers (465 miles) south of Tehran. Construction on the plant began under Iran's Shah Mohammad Reza Pahlavi in the mid-1970s. After the 1979 Islamic Revolution, the plant was repeatedly targeted in the Iran-Iraq war. Russia later completed construction of the facility.

Iran is building two other reactors like it at the site. Bushehr is fueled by uranium produced in Russia, not Iran, and is monitored by the United Nations' International Atomic Energy Agency.

The Arak heavy water reactor is 250 kilometers (155 miles) southwest of Tehran. Heavy water helps cool nuclear reactors, but it produces plutonium as a byproduct that can potentially be used in nuclear weapons. That would provide Iran another path to the bomb beyond enriched uranium, should it choose to pursue the weapon. Iran had agreed under its 2015 nuclear deal with world powers to redesign the facility to relieve proliferation concerns.

The facility in Isfahan, some 350 kilometers (215 miles) southeast of Tehran, employs thousands of nuclear scientists. It also is home to three Chinese research reactors and laboratories associated with the country's atomic program.

The Tehran Research Reactor is at the headquarters of the Atomic Energy Organization of Iran, the civilian body overseeing the country's atomic program. The U.S. actually provided Iran the reactor in 1967 as part of America's "Atoms for Peace" program during the Cold War. It initially required highly enriched uranium but was later retrofitted to use low-enriched uranium over proliferation concerns.