Top Western diplomats flew to Geneva Friday as it appeared that Iran and western nations might be getting closer to an historic deal on Tehran's nuclear programme.
Following are major events regarding the issue over the past 10 years.
Western countries have long suspected that Iran is developing nuclear weapons while Tehran claims it only wants to pursue its programme for civilian use.
The International Atomic Energy Agency (IAEA) reveals in August that traces of enriched uranium have been identified in Natanz, central Iran, where satellite images published by US media in late 2002 revealed a nuclear installation.
Following an unprecedented visit by foreign ministers from Britain, France and Germany in October, Iran suspends uranium enrichment activities. The Iranian pledge to suspend work is repeated in November 2004 but Tehran also says it will "never renounce" the controversial nuclear fuel activities.
On August 8, after the election of hardline president Mahmoud Ahmadinejad, Iran resumes work on the uranium enrichment process at Isfahan, central Iran.
Britain, France and Germany, which had been holding talks with Tehran, break them off. The IAEA, the UN atomic agency, issues a condemnation of Iran in September.
In late 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.
On April 11, Iran says that it has enriched uranium to the point where it contains 3.5 percent of the crucial isotope uranium 235, needed for nuclear fuel.
On June 6, the five permanent UN Security Council members and Germany (P5+1) press Tehran to suspend its enrichment and reprocessing activities and accept a monitoring mechanism in exchange for trade advantages and light water reactors to provide electricity.
On August 22, Iran rejects the offer.
On December 23, the UN imposes the first of several rounds of sanctions on Iran's trade in sensitive nuclear materials and technology.
The sanctions are strengthened several times, notably owing to separate decisions taken by the European Union (EU) and the United States (US).
On November 7, Iran says it has acquired at least 3,000 centrifuges for uranium enrichment, which in theory would allow it to produce enough enriched uranium for a nuclear bomb in less than a year. It now has 19,000.
In December, a report compiled by US information agencies concludes that Iran abandoned plans to develop nuclear weapons in 2003, but acknowledges that they do not know Iran's present intentions.
On June 14, the P5+1 present a new offer to Tehran, but Ahmadinejad vows that the Iranian people "will not step back an inch".
Following the election of US President Barack Obama, who reaches out to Iran, the P5+1 offers on April 8 to resume negotiations with Tehran.
The next day, Iran declares major advances in its nuclear programme as Ahmadinejad opens a uranium enrichment site in Isfahan.
On September 25, western nations reveal the existence of a secret enrichment site in Fordo, inside a mountain near the central holy city of Qom.
On October 1, resumed negotiations in Geneva between Iran and the P5+1 result in an agreement in principle for Iranian uranium to be enriched to 20 percent of uranium 235 abroad for use in Iranian research reactors.
But a final agreement is not reached.
On February 9, Iran says it has begun to enrich uranium to 20 percent at Natanz.
On May 17, Tehran proposes a deal with Brazil and Turkey to enrich its uranium abroad, but the offer is rejected by leading western nations.
Talks between Iran and the P5+1 break down once again on January 22, leading the EU to slap an embargo on Iran's oil exports.
On September 4, Iran hooks up its nuclear power plant in Bushehr to the national grid. On November 8, the IAEA points to a possible military dimension to Iran's nuclear programme.
On January 9, the IAEA says that Iran has begun to enrich uranium to 20 percent at Fordo.
Talks between Tehran and the P5+1 resume on April 14 after a pause of 15 months.
On November 16, the IAEA says that the installation of equipment at the Fordo plant is now "complete", allowing Iran to significantly boost enrichment.
The P5+1 tables a new proposal on February 26 in Almaty, Kazakhstan that would require only a suspension of Iran's uranium enrichment activities. The talks break down on April 6-7.
Obama says on March 14 that Iran is "over a year or so" from getting a nuclear bomb.
On August 6, newly-elected Iranian President Hassan Rouhani says Tehran is ready for "serious" negotiations "without wasting time".
Rouhani reveals in a tweet on September 27 that he and Obama have spoken by telephone in the highest-level contact between the two countries since 1979.
At the same time, a ministerial-level meeting between Iran and the six world powers takes place in New York.
Negotiations in Geneva on October 15-16 appear to make progress and continue on November 7-8, when the foreign ministers of France, Germany and the United States were due to take part.