Iran joins nuclear non-proliferation treaty (NPT).
The rebel group National Council for Resistance in Iran reveals the existence of undeclared nuclear sites, including an enrichment plant in Natanz and a heavy-water production plant in Arak. Iran acknowledges existence of the sites and asks the International Atomic Energy Agency (IAEA) to inspect them.
The IAEA rebukes Iran for not declaring the plant, but does not find it in violation of the NPT.
Iran agrees to suspend uranium enrichment and to allow a regime of unannounced IAEA inspections.
The IAEA finds Iran in non-compliance with the NPT, because of failure to report its nuclear activities.
The US Security Council imposes the first set of sanctions on Iran for its refusal to accept a resolution calling for a suspension of enrichment.
Iran breaks the IAEA seals on the Natanz plant and other nuclear sites.
The IAEA reports Iran to the UN Security Council for non-compliance.
The UN imposes its first round of sanctions, resolution 1737, which called on states to block Iran’s import and export of “sensitive nuclear material.”
A US national intelligence estimate concludes that Iran had stopped its weapons development program in 2003.
US President Barack Obama, then-UK prime minister Gordon Brown and French President Nicolas Sarkozy announce that their intelligence agencies have found a new Iranian enrichment plant dug into the side of a mountain near Qom, at a site called Fordow. Iran had revealed its existence to the IAEA days earlier, but Western officials say that was because it knew it had been discovered.
An apparent breakthrough at a meeting in Geneva, in which Iran agreed to export 1,200kg of its low-enrichment uranium, 75 percent of the total, in return for foreign-made, 20 percent-enriched fuel rods for the Tehran Research Reactor (TRR). The deal breaks down three weeks later in Vienna.
Iranian President Mahmoud Ahmadinejad announces that Iran has made its own 20 percent-enriched uranium
Brazil and Turkey broker a deal on the TRR fuel swap along the same lines as the Geneva proposal. However, the US and its allies reject the deal as too late, in view of Iran’s nuclear progress since Geneva.
An attempt to restart international negotiations on the Iranian nuclear program breaks down in Istanbul.
The IAEA issues a report citing extensive evidence of past work on nuclear weapons, confirming that Iran had tripled its production of 20 percent uranium and made the underground Fordow site fully operational.
IAEA inspectors visit Tehran to investigate evidence pointing to a past weapons program, but say they did not receive sufficient co-operation.