Iran's disputed nuclear program includes uranium enrichment, electricity generation and research at several facilities. They are operating under international inspection or are in the process of being built. Here is an overview of Iran's main nuclear facilities:

Natanz Uranium Enrichment Facility

Iran's uranium enrichment program is based in the central city of Natanz. The site contains an underground plant in which thousands of centrifuges are purifying, or enriching, uranium for use as a nuclear fuel. Low-enriched uranium is sufficient as a fuel for nuclear power plants. Highly-enriched uranium can be used to make nuclear weapons.

The watchdog Institute for Science and International Security says many of the Natanz centrifuges are old and breaking down repeatedly, in part due to the impact of the Stuxnet computer virus that began infecting the facility in late 2009. Iran has been trying to install better centrifuges to expand enrichment, but international sanctions have made it difficult to secure the necessary equipment.

Fordo Uranium Enrichment Facility

Iran disclosed the existence of another uranium enrichment facility at the Fordo site near the Shi'ite holy city of Qom in 2009. The plant is located under a mountain. In September 2011, the International Atomic Energy Agency said Iran had installed a set, or “cascade” of centrifuges at the site. It is not clear how many of the machines are operational.

Bushehr Nuclear Plant

Iran connected its first nuclear power plant to the national electricity grid in the southern city of Bushehr in September after years of delay. Iran said the Russian-built plant was supplying 60 megawatts of power, a small part of its 1,000 megawatt capacity. Iranian President Mahmoud Ahmadinejad said the country needs 20 times more energy than Bushehr was generating.

Russia began construction of the plant in 1995 and said it would supply the enriched uranium needed to fuel it. Iran agreed to send spent fuel to Russia to ensure that it cannot be reprocessed into plutonium, another nuclear weapon ingredient.

Tehran Research Reactor

Iran has been operating a nuclear research reactor in Tehran with low-enriched uranium supplied by Argentina since 1993. Iranian officials have said they need to supply the reactor with higher-enriched uranium because the Argentine fuel reserves were nearly depleted. Iran says the reactor is used for medical purposes and other research.

Isfahan Nuclear Technology Center/Research Reactors

Iran operates several Chinese-built nuclear research reactors in the central region of Isfahan.

Arak Heavy Water Production Plant & Reactor

Iran is building a nuclear reactor that uses heavy water as a coolant in the western region of Arak. Iranian officials have said the reactor will be completed in 2013, but international monitors say the date could be delayed because of problems in securing equipment from overseas.

Darkhovin Nuclear Reactor

Iran also is building its first domestically-designed nuclear power plant in the southwestern city of Darkhovin. It says the facility will have a capacity of 360 megawatts.