The allegation that civilians in the Iraqi city of Fallujah in 2004 were burned to death by the United States military's use of white phosphorous has highlighted a weapon that dates back to before World War I.
For decades, gunners on the battlefield have used white phosphorous rounds as a way to set enemy positions on fire - as well as to provide smoke to cover advancing troops. Although they involve a chemical process, white phosphorous rounds are not classified as chemical weapons, and they are seen among weapons experts as no more inherently sinister than any other conventional weapon.
Yet the claims made by an Italian television station - that women and children were found with melted skin despite the fact that their clothes were unharmed - are consistent with the action of white phosphorous, scientists say.
In an offensive that involved targeting insurgents who were hidden in a city of 500,000 inhabitants, the allegations - if true - do not prove or disprove military malfeasance.
But they do raise the issue of the military's judgment. Because fires can burn out of control during a battle, the Convention on Conventional Weapons in 1980 banned the use of incendiary devices, like white phosphorous, in heavily populated areas. America, however, did not sign the agreement.
In a war that has already brought grotesque evidence of prisoner abuse and is subject to conflicted opinions at home, the reports are another blow to the military and a reminder of the brutal nature of war - and they could heighten the question of whether the American public has the will to continue.
"The problem is war," says Ivan Oelrich, a weapons expert at the Federation of American Scientists here. "Appalling things happen in war, and that's the bigger issue."
This week, the Pentagon acknowledged that it used white phosphorous rounds against insurgents during the battle of Fallujah last November. To some, its use in the middle of a city - even if America didn't sign the 1980 conventional-weapons pact - is irresponsible.
"If white phosphorous [is to be] used as an incendiary, the military has to do so in a manner consistent with our obligations to not unnecessarily harm civilians," says Daryl Kimball, executive director of the Arms Control Association here. "The evidence available suggests that that may not have been done."
Pentagon officials insist that the weapon was not used against civilians. If civilians were indeed killed, as the Italian report alleges, the military will have to determine if the appropriate precautions were taken.
To determine the facts, some observers have called for an investigation, and the Iraqi Health Ministry has already started one of its own.
Yet regardless of what lies ahead, the report has the possibility of becoming to the Iraq war what the famous picture by Nick Ut was to the Vietnam War. In that black-and-white photograph, a young girl runs naked from a napalm attack in Vietnam.
"Obviously, napalm was not [intended] to bomb little girls," says Loren Thompson, a defense analyst at the Lexington Institute in Arlington, Va. "But war is a chaotic affair."
Some experts find it curious that white phosphorous should be so demonized. While it can have terrible effects, it is not seen within the military world as more dangerous or cruel than any other weapon. "Every military uses white phosphorous," says Dr. Oelrich.
If it can be proved that a member of the US military knowingly used it against civilians, it would be a clear violation of international standards. But cries that equate America's use of white phosphorous with Saddam Hussein's use of chemical weapons strikes some as inappropriate.
"It's clear that the European media want to have a fight," says Michael O'Hanlon, a defense analyst at the Brookings Institution here. "The instinct for America-bashing is not helpful."