Iran and six powers failed on Monday for a second time this year to resolve their 12-year stand-off over Tehran's nuclear ambitions, and gave themselves seven more months to clinch an historic deal.

2003

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 program.

2006

December 23: The U.N. imposes the first of several rounds of sanctions on Iran's trade in sensitive nuclear materials and technology.

2007

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.

2009

April 8: 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.

2010

February 9: Iran says it has begun to enrich uranium to 20 percent at Natanz, close to the level required for a nuclear weapon.

2012

January 23: After talks break down again, the EU slaps an embargo on Iranian oil exports.

2013

September 27: Rouhani reveals he and Obama have spoken by telephone in the highest-level contact between the two countries since 1979.

November 24: Iran agrees to curb its nuclear program in exchange for sanctions relief in a preliminary deal which comes into force on January 20.

2014

February 18: Negotiations start on a permanent accord.

November 5: Obama says the U.S. 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 24: Iran and world powers fail in a push to seal a landmark nuclear deal and the talks will be held either in March 1 or July 1.