Aug. 2002 - Exiled opposition group, National Council of Resistance of Iran, reports existence of uranium enrichment facility at Natanz and heavy water plant at Arak.

Dec. 2002 - United States accuses Iran of "across-the-board pursuit of weapons of mass destruction".

June 2003 - International Atomic Energy Agency (IAEA) report, after February inspection of Natanz and Arak, says Iran has failed to comply with nuclear Non-Proliferation Treaty.

Oct. 2003 - Iran tells France, Britain and Germany, the trio negotiating for the European Union, it will suspend all enrichment-related activities.

Dec. 2003 - Iran signs protocol allowing snap inspections of nuclear facilities.

June 2004 - IAEA board complains of inadequate cooperation from Iran. Iran responds by saying it will resume production and testing of centrifuges.

Nov. 2004 - Iran promises EU negotiators it will suspend all nuclear fuel processing and reprocessing work.

Feb. 2005 - President Mohammad Khatami says no Iranian government will give up nuclear technology programmes.

-- Sept. 2 - Report by IAEA chief Mohamed ElBaradei confirms Iran has resumed uranium conversion at Isfahan.

Jan. 1, 2006 - Iran says it has developed machinery to separate uranium from its ore.

-- Jan. 10 - Iran removes UN seals at Natanz and resumes research on nuclear fuel despite Western warnings it would endanger efforts to find compromise.

-- Jan. 12 - EU trio calls off talks with Iran and says nuclear case should be referred to UN Security Council.

-- Feb. 4 - IAEA votes to report Iran to Security Council over suspicions it plans to build atomic weapons. Iran ends snap UN nuclear checks the next day.

-- Feb. 14 - Iran restarts small-scale feeding of uranium gas into enrichment centrifuges at Natanz after 2-1/2-year suspension.

-- March 8 - IAEA sends report to Security Council saying it could not verify Iran's atomic activities are peaceful. Iran warns it can inflict "harm and pain" to match any punitive UN action. However, four days later Tehran says it will not use oil exports as political tool.

-- March 24 - Diplomats say Iran is rapidly expanding uranium enrichment programme.

-- March 29 - Security Council unanimously adopts "presidential statement" calling on Iran to freeze its uranium enrichment work, and asking IAEA to report in 30 days on Iranian cooperation with agency demands.

-- April 12 - Ahmadinejad says Iran has enriched uranium to a level used in power stations. This draws rebukes from world powers, including Russia and China.