- August: The International Atomic Energy Agency (IAEA) reveals that traces of enriched uranium have been identified in Natanz, central Iran, after an Iranian exiled opposition group in 2002 revealed the existence of a nuclear installation.
- October: Following an unprecedented visit by foreign ministers from Britain, France and Germany, Iran suspends uranium enrichment activities but later vows it will never renounce its nuclear programme.
- August 8: After the election of hardline president Mahmoud Ahmadinejad, Tehran resumes uranium enrichment in Isfahan, central Iran.
- January: The UN Security Council's five permanent members -- Britain, China, France, Russia and the United States -- agree to have the IAEA present the issue to the full Council.
- June 6: The permanent members plus Germany, dubbed P5+1, propose a framework for talks but Iran later rejects the offer.
- December 23: The UN imposes the first of several rounds of sanctions on Iran's trade in sensitive nuclear materials and technology.
- November 7: Iran says it has at least 3,000 centrifuges for enrichment, which in theory would allow it to produce enough enriched uranium for a nuclear bomb in less than a year.
April 8: Following the November election of US President Barack Obama, world powers offer to resume negotiations with Tehran, which later declares major advances in its nuclear drive as Ahmadinejad opens a uranium enrichment site in Isfahan.
- September 25: Western nations reveal the existence of a previously undeclared enrichment site inside a mountain in Fordo.
- October 1: Negotiations resume, with an agreement in principle for Iranian uranium to be enriched abroad, but a final deal is not reached.
- February 9: Iran says it has begun to enrich uranium to 20 percent at Natanz, close to the level required for a nuclear weapon.
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- November 8: The IAEA points to a possible military dimension to Iran's nuclear activities.
- January 23: After talks break down again, the EU slaps an embargo on Iranian oil exports.
- August 6: Newly-elected President Hassan Rouhani says Tehran is ready for "serious" negotiations.
- September 27: Rouhani reveals he and Obama have spoken by telephone in the highest-level contact between the two countries since 1979.
- October 14: Negotiations resume
- November 24: Iran agrees to curb its nuclear programme in exchange for sanctions relief in a preliminary deal which comes into force on January 20.
- February 18: Negotiations start on a permanent accord.
- July 18: Iran and world powers agree to extend the deadline for a permanent deal to November 24.
- November 5: Obama says the US has put forward a "framework" plan to meet Iran's energy needs. Two days later the IAEA says Iran is still failing to provide answers in its probe into possible military dimensions.
- November 11: Russia signs a deal with Iran to build two new nuclear reactors and agrees to expand the total to nine.
- November 18: Iran and the six world powers begin a final round of talks.
- November 24: Iran and world powers fail in a push to seal a landmark nuclear deal, giving themselves until March 1 to agree an outline accord and until July 1 -- or seven more months -- to reach a full technical accord.