TIMELINE: Iran's nuclear program

(Reuters) - Six world powers agreed on Friday to push ahead with a third round of tougher sanctions against Iran unless reports later this month indicate Tehran has tried to address their concerns about its nuclear program.

Here is a chronology since it emerged that Iran was carrying out sensitive work that it could use to make atomic bombs. Tehran insists its activities are peaceful:

August 2002 - The exiled opposition National Council of Resistance of Iran reports the existence of uranium enrichment facility at Natanz and heavy water plant at Arak.

December 2002 - The 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.

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

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

September 2, 2005 - IAEA report confirms Iran has resumed uranium conversion at Isfahan.

January 10, 2006 - Iran removes U.N. seals at Natanz enrichment plant and resumes nuclear fuel research.