August 2002 -- An Iranian exile opposition group, the National Council of Resistance of Iran, accuses Tehran of hiding a uranium-enrichment facility at Natanz and a heavy-water plant at Arak.
February 2003 -- International Atomic Energy Agency (IAEA) Director-General Muhammad el-Baradei visits Iran to verify Tehran's claims that its nuclear program is peaceful. IAEA inspectors later find traces of highly enriched uranium at Natanz and other sites.
June 2003 -- In a report, el-Baradei says inspections have demonstrated that "Iran failed to report certain nuclear materials and activities" and urges Tehran to cooperate with the agency. The report does not declare Iran in breach of the Nuclear Nonproliferation Treaty (NPT). The IAEA requests that Iran sign on to the Additional Protocol to the NPT and allow unannounced inspections of its nuclear sites.
July 2003 -- IAEA begins a fresh round of inspections in Iran.
September 2003 -- The United States says Iran is in noncompliance with the NPT, and calls for a referral to the UN Security Council, which could impose sanctions. But Washington agrees to support a proposal from Great Britain, France, and Germany (who were negotiating on behalf of the European Union and became known as the "EU Three") to give the Tehran until the end of October to fully disclose nuclear activities and allow for a stricter inspection regime.
October 2003 -- The foreign ministers of France, Germany, and Great Britain travel to Tehran and persuade Iran to agree to stop enriching uranium and to sign the Additional Protocol to the NPT. The EU Three also dangle economic concessions if Tehran cooperates fully with the IAEA. Iran turns over a declaration to the IAEA admitting to 18 years of covert atomic experiments, including the unreported uranium enrichment, although it continues to deny this was for a weapons program.
November 2003 -- An IAEA report states that at the moment there is no conclusive proof that Iran is developing nuclear weapons. The United States, seeking to have Iran sent to the UN Security Council, dismisses the conclusion. The IAEA's 35-menber board of governors passes a resolution sternly rebuking Iran for covering up 18 years of atomic experiments, but does not send the matter to the Security Council.
February 2004 -- Abdul Qadeer Khan, the founder of Pakistan's nuclear program, says that he had provided atomic secrets to Iran, Libya, and North Korea since the late 1980s. IAEA inspectors notice similarities in designs and components for the advanced P-2 centrifuge, adding to suspicions that Khan supplied both countries with same nuclear know-how.
May 2004 -- Iran submits to the IAEA a over-1,000-page report on its nuclear activities.
June 2004 -- IAEA says that inspectors found new traces of enriched uranium that exceeded the levels necessary for civilian energy production.
July 2004 -- Iran says it has resumed production of parts for centrifuges that are used for enriching uranium, but insists that it has not resumed its enrichment activities. The announcement appears to put the enrichment-freeze deal worked out between Iran, the EU Three, and the IAEA in jeopardy.
September 2004 -- An IAEA report calls Iran's claims about its nuclear program "plausible," but voices concern over Iran's decision to resume large-scale production of the feed material for enriching uranium. Claiming enrichment is a "sovereign right," Iran refuses to accept an unlimited suspension and says it will not stop manufacturing centrifuges. The IAEA gives Iran a 25 November deadline to reveal all its nuclear activities. Tehran later announces that it has resumed large-scale conversion of uranium yellowcake ore, a step towards uranium enrichment.
October 2004 -- The EU Three again calls for Iran to suspend all uranium-enrichment activities to avoid its case being brought before the Security Council. The Europeans offer economic and political incentives in exchange. The Iranian parliament passes a bill approving the resumption of enrichment activities.
November 2004 -- Iran holds talks in Paris with the EU Three. On 14 November, Iran signs an agreement to suspend uranium enrichment. The Europeans offer a series of political and economic concessions in exchange. But at an IAEA board of governors meeting from 25-29 November -- which was set to pass a resolution endorsing the deal and agreeing to monitor it -- Iran insists on an exemption for 20 centrifuges for research purposes. Iran eventually backs down, but demands -- and wins -- key changes softening the resolution in exchange. Most importantly, the resolution describes the enrichment freeze as a voluntary, rather than the legally binding commitment as both the United States and the EU sought.
December 2004 -- Talks between Iran and the EU Three over political and economic concessions, in exchange for Iran making its enrichment suspension permanent, are scheduled to begin on 13 December.