Iran's nuclear program has advanced on many fronts in the past decade. Here's a look at its program:

RAISED AT TALKS

Arak heavy water reactor: Such reactors can run on non-enriched uranium as fuel and use a molecular variant of water as a coolant. Heavy water reactors also produce more plutonium byproducts than conventional reactors. Plutonium can be used in nuclear weapons. Iran began work on its facility in 2004 in Arak, about 150 miles southwest of Tehran. U.N. nuclear inspectors have visited the site, but have been promised wider access under the latest accord between Iran and the U.N.'s International Atomic Energy Agency, or IAEA. The reactor is nearing completion, but no specific date has been announced to begin operations. Iran says the reactor will be used to produce isotopes for medical and industrial uses.

Enrichment sites: Iran has two main uranium enrichment facilities. The oldest and largest — in Natanz, about 160 miles southeast of Tehran — is largely built underground and is surrounded by anti-aircraft batteries. Uranium enrichment began in 2006. Another site is known as Fordo, which is built into a mountainside south of Tehran. Its construction was kept secret until September 2009.

OTHER REACTORS

Bushehr: Iran's first energy-producing nuclear reactor, which began full operations in early 2013.

Tehran: The main research reactor is in Iran's capital, mainly involved in producing isotopes for cancer treatment.

Planned: The most discussed proposal is an energy-producing reactor in Darkhovin, built entirely with domestic technology.

URANIUM MINES AND PROCESSING

Saghand: Uranium mine in Yazd province is the principal source of uranium ore.

Gachin: A smaller uranium mining site and processing facility near Bandar Abbas on the Persian Gulf.

Ardakan: A planned plant for processing uranium ore into yellowcake, a uranium concentrate that is the basic feedstock in the steps to make nuclear fuel. The plant, about 300 miles southeast of Tehran, is not yet in operation. The other site, Gachin, has produced small amounts of yellowcake since 2006.

Isfahan uranium conversion facility: A plant that reprocesses yellowcake into a gas, which is then fed into centrifuges for enrichment. A separate facility in Isfahan produces non-enriched fuel for the Arak reactor.

DISPUTED SITE

Parchin military base: It has been suspected of housing a secret underground facility used for blast tests related to potential nuclear triggers.

Associated Press