1991: The International Atomic Energy Agency placed a seal over storage bunkers holding conventional explosives known as HMX and RDX at the Al-Qaqaa facility south of Baghdad as part of U.N. sanctions that ordered the dismantlement of Iraq's nuclear program after the Gulf War. HMX is a ''dual use'' substance powerful enough to ignite the fissile material in an atomic bomb and set off a nuclear chain reaction.

January 2003: IAEA inspectors viewed the explosives at Al-Qaqaa for the last time. The inspectors took an inventory and again placed storage bunkers at Al-Qaqaa under agency seal.

February 2003: IAEA chief Mohamed ElBaradei told the United Nations that Iraq had declared that ''HMX previously under IAEA seal had been transferred for use in the production of industrial explosives.'' This apparently did not include the HMX that remained under seal at Al-Qaqaa.

March 2003: Nuclear agency inspectors visited Al-Qaqaa for the last time but did not examine the explosives because the seals were not broken. The inspectors then pulled out of the country.

March 2003: The U.S.-led coalition invaded Iraq.

After the invasion: The Pentagon said Monday that ''coalition forces were present in the vicinity at various times during and after major combat operations. The forces searched 32 bunkers and 87 other buildings at the facility, but found no indicators of WMD (weapons of mass destruction). While some explosive material was discovered, none of it carried IAEA seals.

Oct. 10, 2004: Iraq's Ministry of Science and Technology told the nuclear agency that 377 tons of explosives had disappeared from the Al-Qaqaa facility. The Iraqis said the materials were stolen and looted because of a lack of security.

Oct. 15, 2004: The IAEA informed the U.S. mission in Vienna about the disappearance. National security adviser Condoleezza Rice was informed days later, and she informed President Bush, according to White House press secretary Scott McClellan.

Oct. 23-24, 2004: The Pentagon ordered the U.S. military command in Baghdad and the Iraq Survey Group to investigate the IAEA report, the Pentagon official said, adding it was not clear how or by whom the explosives were taken or whether any of the material had been used in insurgent attacks.

Oct. 25, 2004: ElBaradei reports the explosives' disappearance to the U.N. Security Council after The New York Times reports the cache is missing.