VIENNA, Austria – Here is a summary of the main developments in the 13-year standoff between Iran and the West over Tehran’s disputed nuclear program.
2002-2004: Undeclared sites
In 2002 the existence of undeclared nuclear facilities at Natanz and Arak is revealed. Iran invites the International Atomic Energy Agency (IAEA) to carry out inspections and says its activities are peaceful.
In 2003, Iran agrees with Britain, Germany and France to suspend suspect activities but the following year goes back on the pledge.
In 2004, the IAEA says it found no evidence of a secret weapons drive but cannot rule out undeclared materials. In Paris talks, Iran again agrees to suspend certain activities.
2005-2008: Escalation and enrichment
In August 2005, under a hardline president, Mahmoud Ahmadinejad, Tehran produces uranium gas, the precursor to enrichment for providing the core material for a bomb. European nations break off negotiations.
In 2006, Iran breaks IAEA seals on the Natanz enrichment facility and begins enrichment. The IAEA refers Iran to the UN Security Council, which in July passes the first of seven resolutions.
In August, Ahmadinejad inaugurates a heavy water plant at Arak, raising fears Iran might be seeking weapons-grade plutonium.
December’s second UN Security Council resolution comes with sanctions attached. The US and EU follow suit.
By November 2007, Iran says it has at least 3,000 centrifuges, which in theory would allow it to produce enough enriched uranium for a nuclear bomb in less than a year. In 2015 it had almost 20,000, of which half were active.
2009-2012: Advances and allegations
In September 2009, US, French and British leaders announce Iran is building an undeclared enrichment site at Fordo, built into a mountain near Qom.
In October, Iran agrees to swap low-enriched uranium for reactor fuel. But the deal unravels and in February 2010 Iran begins enriching uranium to close to bomb-grade — providing isotopes for medical use, it says.
In 2011, the Russian-completed Bushehr power reactor — first begun by Germany’s Siemens — begins operating.
In November 2011, an IAEA report, collating “broadly credible” intelligence, says that at least until 2003 Iran “carried out activities relevant to the development of a nuclear explosive device.”
The following month the US Congress passes legislation sanctioning lenders who deal with Iran’s central bank.
In January 2012, the EU bans all member states from importing Iranian oil. Israeli Prime Minister Benjamin Netanyahu, whose country is widely assumed to have nuclear weapons, brandishes a diagram of a bomb at the UN General Assembly, calling for a “clear red line” to be drawn under Iran’s program.
2013: Interim accord
Newly-elected Iranian President Hassan Rouhani vows in 2013 he is ready for “serious” negotiations.
After secret negotiations in Oman between US and Iranian representatives, Rouhani and US President Barack Obama have an unprecedented phone conversation.
In November, an interim deal is agreed freezing some of Iran’s nuclear activities in exchange for minor sanctions relief. Two deadlines — July and November 2014 — to agree on a final deal are missed. In April 2015, Iran and major powers agree in Lausanne, Switzerland on the main outlines of a final deal.
2015: “Historic” accord
On July 14, the accord is finally concluded in Vienna, ending 12 years of crisis and 21 months of protracted negotiations.
The accord provides Tehran relief from crippling economic sanctions in exchange for limits on its nuclear program.
In mid-December, the IAEA draws a line under a long-running probe into Iran’s past efforts to develop nuclear weapons, removing an important obstacle to implementing the July deal.
2016: Implementing the deal
January 14: Iran says it has removed the core of its Arak heavy water reactor and filled part of it with concrete, paving the way for UN nuclear inspectors to announce Tehran has met its commitments.
January 16: The International Atomic Energy Agency confirms that Iran has “carried out all measures required under the (July deal)… to enable Implementation Day to occur.”