Italian state TV, Rai, has broadcast a documentary accusing the US military of using white phosphorus bombs against civilians in the Iraqi city of Falluja.
The US assault began exactly a year ago
Rai says this amounts to the illegal use of chemical arms, though the bombs are considered incendiary devices.
Eyewitnesses and ex-US soldiers say the weapon was used in built-up areas in the insurgent-held city.
The US military denies this, but admits using white phosphorus bombs in Iraq to illuminate battlefields.
Washington is not a signatory of an international treaty restricting the use of white phosphorus devices.
Spontaneously flammable chemical used for battlefield illumination
Contact with particles causes burning of skin and flesh
Use of incendiary weapons prohibited for attacking civilians (Protocol III of Convention on Certain Conventional Weapons)
Protocol III not signed by US
Transmission of the documentary comes a day after the arrival of Iraqi President Jalal Talabani on a five-day official visit to Italy.
It also coincides with the first anniversary of the US-led assault on Falluja, which displaced most of the city's 300,000 population and left many of its buildings destroyed.
The documentary was shown on Rai's rolling news channel, with a warning that the some of the footage was disturbing.
The future of the 3,000-strong Italian peacekeeping contingent in Iraq is the subject of a political tug-of-war, says the BBC's David Willey in Rome.
The documentary begins with formerly classified footage of the Americans using napalm bombs during the Vietnam war.
It then shows a series of photographs from Falluja of corpses with the flesh burnt off but clothes still intact - which it says is consistent with the effects of white phosphorus on humans.
Jeff Englehart, described as a former US soldier who served in Falluja, tells of how he heard orders for white phosphorus to be deployed over military radio - and saw the results.
"Burned bodies, burned women, burned children; white phosphorus kills indiscriminately... When it makes contact with skin, then it's absolutely irreversible damage, burning flesh to the bone," he says.
Last December, the US state department issued a denial of what it called "widespread myths" about the use of illegal weapons in Falluja.
"Phosphorus shells are not outlawed. US forces have used them very sparingly in Falluja, for illumination purposes. They were fired into the air to illuminate enemy positions at night, not at enemy fighters," the US statement said.
However, the Rai film also alleges that Washington has systematically attempted to destroy filmed evidence of the alleged use of white phosphorus on civilians in Falluja.
Italian public opinion has been consistently against the war and the Rai documentary can only reinforce calls for a pullout of Italian soldiers as soon as possible, our correspondent says.
Both the Italian government and opposition leaders are talking about a phased withdrawal in 2006.
President Talabani and the US say the continued presence of multi-national forces in Iraq is essential.