World powers are locked in crunch talks with Iranian negotiators in Vienna amid efforts to resolve a decade-long stand-off over Tehran’s nuclear ambitions.
Doubts are growing that a November 24 deadline for a comprehensive deal will be met at the talks in the Austrian capital.
The US, Britain, France, Germany, along with Russia and China, want Iran to curb its disputed nuclear programme, saying they will lift United Nations sanctions in return.
On Sunday, US and German diplomats said the sides were working to close "big gaps", with some suggestions that the deadline could be extended.
Reporting from Vienna, FRANCE 24’s Sanam Shantyaei says “it is not clear whether this is part of brinkmanship or whether the Iranian team actually has a mandate to reach a deal.”
Western countries have long suspected that Iran is developing nuclear weapons while Tehran claims it only wants to pursue its programme for civilian use.
An Iranian source on Sunday said Tehran is open to extending the negotiations by six months or a year if no real progress toward an agreement is achieved by the end of this weekend.
The following are major events regarding the issue over the past 10 years.
2002 - 2005: First traces
The International Atomic Energy Agency (IAEA) revealed in August 2003 that traces of enriched uranium were 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 announced it was suspending uranium enrichment activities.
The Iranian pledge to suspend work was repeated in November 2004 but Tehran insisted it would "never renounce" the controversial nuclear fuel activities.
2005 - 2011: The tone hardens, sanctions are imposed
On August 8, 2005, after the election of hardline president Mahmoud Ahmadinejad, Iran resumed work on the uranium enrichment process at Isfahan, central Iran.
Britain, France and Germany, which had been holding talks with Tehran, broke them off. The IAEA, the UN atomic agency, issued a condemnation of Iran in September.
On April 11, Iran said that it had enriched uranium to the point where it contained 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) pressed Tehran to suspend its enrichment and reprocessing activities and accepted a monitoring mechanism in exchange for trade advantages and light water reactors to provide electricity. The Iranians rejected the offer.
On December 23, the UN imposed the first of several rounds of sanctions on Iran's trade in sensitive nuclear materials and technology.
On November 7, 2007, Iran said it had 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 concluded that Iran abandoned plans to develop nuclear weapons in 2003, but acknowledged that they did not know Iran's present intentions.
On June 14, 2008, the P5+1 presented a new offer to Tehran, but Ahmadinejad vowed that the Iranian people would “not step back an inch".
Following the election of US President Barack Obama, who reached out to Iran, the P5+1 offered on April 8 to resume negotiations with Tehran.
The next day, Iran declared major advances in its nuclear programme as Ahmadinejad opened a uranium enrichment site in Isfahan.
On September 25, western nations revealed 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 resulted in an agreement in principle for Iranian uranium to be enriched to 20 percent abroad for use in Iranian research reactors. A final agreement was not reached.
On February 9, 2010, Iran said it had begun to enrich uranium to 20 percent at Natanz.
On May 17, Tehran proposed a deal with Brazil and Turkey to enrich its uranium abroad, but the offer was rejected by leading western nations.
2011 - 2013: International sanctions to the election of Rohani
Talks between Iran and the P5+1 broke down once again on January 22, 2011, leading the EU to slap an embargo on Iran's oil exports.
On September 4, Iran hooked up its nuclear power plant in Bushehr to the national grid. On November 8, the IAEA pointed to a possible military dimension to Iran's nuclear programme.
On January 9, 2012, the IAEA said that Iran had begun to enrich uranium to 20 percent at Fordo.
Talks between Tehran and the P5+1 resumed on April 14 after a pause of 15 months.
On November 16, the IAEA said that the installation of equipment at the Fordo plant was now "complete", allowing Iran to significantly boost enrichment.
The P5+1 tabled a new proposal on February 26, 2013, in Almaty, Kazakhstan, that required only a suspension of Iran's uranium enrichment activities. The talks broke down on April 6-7.
On August 6, newly-elected Iranian President Hassan Rohani announced that Tehran was ready for "serious" negotiations "without wasting time".
Rouhani revealed in a tweet on September 27 that he and Obama had spoken by telephone in the highest-level contact between the two countries since 1979.
In November, Iran and the six world powers made a first breakthrough by clinching an interim deal to freeze Iran’s nuclear programme. The deal set a July 2014 deadline for a final agreement.
In January 2014, Western powers lifted a first batch of sanctions as a sign of encouragement, but Republican lawmakers in the US Congress threatened to impose new sanctions on Iran.
In July, the deadline to reach a final deal was extended until November 24, giving all parties more time to try to bridge major differences over whether Iran will be forced to dismantle parts of its nuclear infrastructure.
Watch FRANCE 24's special report: Inside an Iranian nuclear research reactor
Date created : 2013-11-09