VIENNA, Austria - U.S. officials were warned about the vulnerability of explosives stored at Iraq's Al-Qaqaa military installation after another facility - the country's main nuclear complex - was looted in April 2003, the U.N. nuclear agency said Thursday.

The International Atomic Energy Agency cautioned American officials directly about what was kept at Al-Qaqaa, the main storage facility in Iraq for so-called high explosives, spokeswoman Melissa Fleming said.

The disclosure shed new light on what the United States knew about Al-Qaqaa, which held 377 tons of high explosives that have vanished - an issue that has become a flashpoint in the final days of the U.S. presidential campaign.

The explosives can be used to make car bombs that insurgents have used to target U.S.-led forces in Iraq. On Thursday, an armed group in Iraq claimed in a video to have obtained a large amount of the missing material - HMX, RDX and PETN - and threatened to use it against foreign troops.

Iraqi officials say the materials were taken amid looting sometime after the fall of Baghdad to U.S. forces on April 9, 2003, though the Pentagon and President Bush are suggesting the ordnance could have been moved before the United States invaded on March 20, 2003.

An IAEA official told The Associated Press the explosives were stored in hundreds of large, heavy cardboard drums that probably would have required trucks and forklifts to handle. The U.S. military has said it would be difficult to haul away so much material unnoticed once troops reached the area.

Defense Secretary Donald H. Rumsfeld agreed.

"We would have seen anything like that," he said Thursday in a radio interview at the Pentagon. "The idea it was suddenly looted and moved out, all of these tons of equipment, I think is at least debatable."

Fleming did not say which officials were notified or when, but she said the IAEA - which had put storage bunkers at the site under seal two months before the war - alerted the United States about Al-Qaqaa after the Tuwaitha nuclear complex was looted. The IAEA said it informed U.S. officials separately of the Tuwaitha looting on April 10.

The explosives' disappearance recently has dominated the presidential campaign, with Democratic nominee John Kerry saying the Bush administration's poor planning led to the loss of the dangerous material. The Pentagon contends Saddam Hussein's regime may have removed the explosives before the war.

The IAEA also sought Thursday to clarify reports that the amount of missing explosives may have been far less than what the Iraqis said in an Oct. 10 report to the nuclear agency. ABC News, citing IAEA inspection documents, reported Wednesday that the Iraqis had declared 141 tons of RDX explosives at Al-Qaqaa in July 2002, but that the site held only three tons when it was checked in January 2003. The network said that could suggest that 138 tons were removed from the facility long before the March 2003 invasion.

Vice President Dick Cheney seized upon the ABC report Thursday, telling supporters in Wisconsin that Kerry had gotten the facts wrong in criticizing the Bush administration for the disappearance of the explosives.

But Fleming said most of the RDX - about 125 tons - was kept at Al-Mahaweel, a storage site under Al-Qaqaa's jurisdiction located about 30 miles outside the main Al-Qaqaa site. She also said about 10 tons already had been reported by Iraq as having been used for non-prohibited purposes between July 2002 and January 2003.

"IAEA inspectors were in the process of verifying this statement (the Iraqi inventory of its weapons) ... and would have proceeded later had they stayed in Iraq," Fleming said. The nuclear agency's inspectors pulled out of Iraq just before the invasion and have not been allowed to return for general inspections despite ElBaradei's requests that they be allowed to finish their work.

Agency inspectors have returned twice to Iraq since the war but focused only on Tuwaitha, a nuclear complex 12 miles south of Baghdad. They have not been allowed back to Al-Qaqaa.