Iran and six world powers reached a landmark nuclear deal on Tuesday meant to curb Iran's nuclear program in exchange for sanctions relief. A look at the main points:

— ENRICHMENT: Iran will reduce the number of uranium-enriching centrifuges it has from almost 20,000 to 6,104, and reduce the number of those in use from nearly 10,000 to half that. It also commits to using only its current models, rather than more advanced centrifuges it had wanted to install.

— STOCKPILE: Iran committed to reducing its stockpile of enriched uranium from about five tons to 300 kilograms (less than 700 pounds) for 15 years. U.S. officials say that at this level it would take Iran more than a year to enrich enough uranium for a nuclear weapon.

— UNDERGROUND SITE: Iran committed to convert its Fordo enrichment site — dug deep into a mountainside and thought impervious to air attack — into a research center.

— TRANSPARENCY: Iran will give more access to its nuclear program to the U.N. nuclear agency. If that agency identifies a suspicious site, an arbitration panel with a Western majority will decide whether Iran has to give the agency access within 24 days.

— REACTORS AND REPROCESSING: Iran must redesign its nearly built reactor at Arak so it can't produce plutonium for nuclear weapons.

— SANCTIONS: All U.S. and European Union nuclear-related sanctions will be suspended after experts have verified that Iran is hewing to its commitments. If at any time Iran fails to fulfill its obligations, those sanctions will snap back into place. An arms embargo will stand for five years and restrictions on Iran's ballistic missile programs for eight. Iran will get some access to currently restricted sensitive technologies.