Timeline: A history of Iranian nuclear diplomacy
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As world powers announced on Tuesday that a landmark agreement on Iran's nuclear programme had been reached in Vienna, FRANCE 24 takes a look at the decades-long stand-off over Tehran’s nuclear ambitions.
1953: Under Shah Mohammad Reza Pahlavi, Iran launches a civilian nuclear programme as part of US President Dwight D. Eisenhower's Atoms for Peace initiative, which promoted the use of civilian nuclear technology in less-developed countries. The initiative aimed to conclude non-proliferation agreements with the newly nuclear states that would prevent them from pursuing atomic weapons in the future.
1967: The Tehran Nuclear Research Center is established, its reactor fueled with highly enriched uranium.
1968: Iran and 51 other countries sign the Nuclear Non-Proliferation Treaty, thereby pledging never to become nuclear-weapon states.
1974: The Atomic Energy Organization of Iran is established, which trains personnel and concludes nuclear deals with countries including France, the United States and West Germany. A West German company begins building two light-water reactors at the Bushehr nuclear complex, 760 kms (470 miles) south of Tehran.
1978: After years of refusals from a United States increasingly wary of Iran's ultimate nuclear ambitions, Washington agrees to let Tehran reprocess US-supplied nuclear fuel in exchange for implementing additional safeguards.
US-Iranian cooperation ends
1979: The Islamic Revolution overthrows the Shah, and his successor cancels the $6.2 billion contract for constructing power plants at the Bushehr complex. The United States reneges on its former deal with Tehran and stops supplying enriched uranium for the Tehran research reactor. All nuclear cooperation with the United States is suspended when a hostage crisis erupts in January at the US embassy in Tehran, which lasts until January 1981.
1980-1990: During the Iran-Iraq war (1980-1988) the Ayatollah Khamenei secretly restarts Iran's nuclear programme and seeks German assistance to complete construction at Bushehr. With help from China, Iran establishes a nuclear research facility at Isfahan in 1984 that eventually becomes Iran's second-largest nuclear complex and the suspected focus of the country's efforts to develop nuclear weapons. In the late 1980s, Abdul Qadeer Khan, the father of Pakistan’s nuclear weapons programme, sells uranium enrichment technology to Iran, North Korea and Libya.
1995-1996: Iran announces its intention to sign an $800 million contract with Russia in 1995 to build one of two light-water reactors at the Bushehr nuclear facility. Amid growing fears that Iran is seeking a nuclear weapon, then president Bill Clinton in 1996 imposes US sanctions on foreign companies investing in Iran.
2002: Iranian dissident group Mujahideen Khalq, or the People's Mujahideen of Iran, reveals a clandestine Iranian nuclear programme that includes a uranium enrichment plant at Natanz and a heavy water plant at Arak. Iran agrees to inspections by the UN's International Atomic Energy Agency (IAEA).
2003: The IAEA reveals in August that traces of enriched uranium were identified at Natanz. Following a visit by foreign ministers from Britain, France and Germany in October, Iran announces it is suspending its enrichment activities.
2004: Britain, France and Germany agree to acknowledge Iran's right to pursue a civilian nuclear programme. As part of the "Paris Agreement", Tehran agrees to suspend uranium enrichment for the duration of the talks.
2005: On August 8, just days after the election of hardline president Mahmoud Ahmadinejad, Iran resumes work on the uranium enrichment process at Isfahan in central Iran. Britain, France and Germany suspend talks with Tehran. Ahmadinejad becomes an avid defender of Iran's nuclear programme and sparks concern with his vows to wipe Israel "off the map".
2006: Iran resumes uranium enrichment activities at Natanz after negotiations with EU and US officials collapse. A heavy-water production plant in Arak, 190 kms southwest of Tehran, starts up that could help Iran obtain plutonium, which can be used in both reactors and nuclear weapons.
The UN imposes the first sanctions on Iran's trade in sensitive nuclear materials and technology in December.
2008: International talks end in deadlock over demands that Iran stop enriching uranium. Iranian diplomats say they consider the "right to enrich" issue to be non-negotiable.
2009: The United States joins the international Iran negotiations, which will now be lead by the "P5+1" – the US, the UK, France, China and Russia (as the five permanent members of the UN Security Council) plus Germany. US, British and French officials outline years of Iranian efforts to build a secret enrichment facility inside a mountain at Fordo. But US officials say it will take at least a year and up to five for Iran to make a nuclear weapon.
2010: IAEA inspectors say they have evidence of “past or current undisclosed activities” related to Iran's developing a nuclear payload for a missile. The report also contradicts a 2008 US intelligence assessment that found Iran had suspended work on a bomb in 2003, saying instead that weapons programmes continued "beyond 2004".
The UN Security Council levies a fourth round of sanctions in June that limits the financial activities of Iran's Revolutionary Guards. Iran is banned from investing in overseas enrichment facilities or related technologies.
2011: Western powers move to cut Iran off from the international financial system with coordinated sanctions targeting the central bank as well as private banks. The United States imposes sanctions on companies with links to Iran’s nuclear sector or its key petrochemical and oil industries.
2012: Talks between Iran and the six world powers falter in May, with the P5+1 insisting that Iran halt enriching uranium at 20 percent purity, which is a step away from weapons-grade. Tehran wants an easing of the sanctions and a recognition of its "right to enrich".
An EU embargo on Iranian oil takes effect in July, severely limiting Iran's ability to sell its key export. The United States intensifies sanctions in August aimed at Iran's oil and petrochemical sectors, its two largest exports, as well as its shipping industry. By October, the Iranian rial has fallen by 40 percent.
The European Union also toughens its sanctions against Iran, banning trade in the finance, metals and natural gas sectors.
Iranian oil sales fall by half
2013: Iranian oil exports have dropped by a million barrels a day by February. A new round of US sanctions requires any country purchasing Iranian oil to put the funds into a local bank account, preventing Iran from repatriating the money and limiting it to buying goods within the purchasing country.
By the end of February, Iranian oil sales have been cut in half. Iran meets with the P5+1 in Kazakhstan but talks end without an agreement on curtailing Iranian stockpiles of enriched uranium for a limited lifting of sanctions.
The six powers also agree that Iran can keep a small amount of 20 percent enriched uranium for use in a reactor producing medical isotopes.
The Obama administration imposes new sanctions on Iran four times in one week in June, blacklisting what it says is a network of shell companies controlled by the Iranian leadership, and threatens foreign banks that trade in the Iranian rial.
That same month Iran elects President Hassan Rohani, seen as a moderate. Rohani chooses Mohammad Javad Zarif, a US-educated diplomat, as his foreign minister and to lead the Iranian delegation in nuclear negotiations.
New rounds of talks
Rohani reveals in a September 2013 tweet that he and Obama had spoken by telephone, the highest-level contact between the two countries since the 1979 revolution. Obama confirms at a press conference that the call took place and that the two leaders discussed the ongoing nuclear talks.
The IAEA says in November that Iran will permit “managed access” by international inspectors to two key nuclear facilities but not to the Parchin military site. On November 24, Iran and the six world powers agree an interim deal to halt Iran’s nuclear programme. The agreement will extend for six months, at which point it is hoped a more lasting accord can be reached.
Washington unveils new sanctions against more than a dozen companies and individuals linked to Iran's nuclear programme in December.
A July deadline for a final deal is extended until November, giving the parties more time to overcome persistent differences over dismantling parts of Iran's nuclear infrastructure, allowing inspections and the speed at which to roll back sanctions.
On November 24 the year-long effort fails to reach a permanent accord and the P5+1 declare a seven-month extension.
2015: Nuclear talks in Lausanne, Switzerland, go past a self-imposed preliminary deadline on March 31 as negotiators fail to agree on key issues, including whether Iran remains willing to send its enriched stockpiles to Russia for storage.
The negotiating parties announce on April 2 that "key parameters" have been agreed, including slashing by more than half the number of centrifuges at the Natanz facility to 6,000. The Fordo underground enrichment site will be partly converted into a research facility and the Arak reactor will operate on a limited basis that will not allow it to produce fuel for a bomb.
The European Union and the United States, for their part, will start lifting sanctions as Iran complies with the framework deal to be finalised by a June 30 deadline.
Days before the deadline, both sides in the negotiations said that a lot of "hard work" remained to be done. On June 30, negotiators meeting in Vienna announced that the framework agreement had been extended to July 7 and that the talks would continue.
Diplomats said on July 13 that they were hopeful the talks were reaching their "final stage" after continuing for 17 days, with envoys extending the deadline three times.
On July 14 negotiators announce that a landmark agreement has been reached. Officials say the deal includes allowing UN inspectors to request access to Iranian military sites and calls for sanctions to be reinstated if Iran fails to comply with the terms of the agreement, both major sticking points during the talks.
Watch FRANCE 24's special report: Inside an Iranian nuclear research reactor
For a more detailed look at the negotiations by year, visit the Arms Control Association website by clicking here.