An ABC News report on Wednesday suggested the total may in fact be just three tonnes.
Casting doubt on the Iraqi science ministry declaration of 10 October, the network says it has obtained International Atomic Energy Agency (IAEA) documents that prove its claim.
Dated 14 January 2003 - before the US-led invasion and occupation of Iraq - an IAEA inspector's survey reports just over three tonnes of high explosives were at the al-Qaqaa storage facility, ABC reported.
And several other speculative reports have appeared in the US media, coming at a time when the issue has entered the presidential campaign.
Seemingly unmoved by the ABC revelation, the Washington Times reported on Wednesday that Russian special forces "almost certainly" raided the store before March 2003 and sent the contents to Syria, Lebanon "and possibly even Iran".
Deputy undersecretary of defence for international technology security, John Shaw, told the newspaper: "The Russians brought in, just before the war got started, a whole series of military units ... their main job was to shred all evidence of any of the contractual arrangements they had with the Iraqis."
Dismissing accounts that explosives could have been stolen, Shaw added: "That was such a pivotal location, number one, that the mere fact of [explosives] disappearing was impossible," he said.
"And number two, if the stuff disappeared, it had to have gone before we got there."
But the New York Times appeared to contradict the undersecretary.
Citing three witnesses, the daily said following the US-led invasion, looters stormed the al-Qaqaa facility to haul off "munitions, dismantled heavy machinery and office furniture".
US army Colonel David Perkins, who commanded the brigade that first entered the al-Qaqaa site in March 2003, said on Wednesday his men only conducted a cursory search of the facility because their priority was to continue the march to Baghdad.
"The main focus was
not go back and do a very precise inventory of how many shells and things like that because it was just not the
threat at the time"
Colonel David Perkins,
US commander who captured
al-Qalqaa storage depot
"The main focus was not go back and do a very precise inventory of how many shells and things like that because it was just not the threat at the time," he said.
Democratic presidential candidate Senator John Kerry has raised the disappearance of the high explosives in the campaign for the White House.
Kerry said it was an example of President George Bush bungling the Iraq war. The IAEA, the United Nation's nuclear watchdog, said the site was never secured by the US military after the March 2003 invasion.
Bush accused the Massachusetts senator of making "wild charges" about the missing explosives and told supporters at a Pennsylvania rally on Wednesday that the military was investigating a number of possible scenarios, including that the explosives may have been moved before US troops arrived at the site.