The United States' most senior general has defended the use of weapons containing white phosphorus in Iraq.
White phosphorous being used over Falluja
General Peter Pace said that such munitions were a "legitimate tool of the military", used to illuminate targets and create smokescreens.
Two weeks ago, the US admitted using it to flush out insurgents in Falluja last year - raising concerns that it might have hit civilians.
Initially, the military denied using it against either insurgents or civilians.
Correspondents said having had to retract its original denial was a public relations disaster for the US.
'Within the law'
Gen Pace said no military went to greater lengths to avoid civilian casualties than the US army.
He said white phosphorus, a chemical that burns on exposure to oxygen, producing a bright light and lots of white smoke, was used primarily to illuminate a battlefield or to hide troop movements.
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
"It is not a chemical weapon. It is an incendiary. And it is well within the law of war to use those weapons as they're being used, for marking and for screening," he said.
If it comes into contact with human skin, white phosphorus can ignite and burn down to the bone if it is not exhausted or extinguished.
An Italian TV channel has reported that the US used white phosphorus against civilians in Falluja, and showed pictures of burned bodies.
The US has denied this.
"A bullet goes through skin even faster than white phosphorus does," Gen Pace said.
"So I would rather have the proper instrument applied at the proper time, as precisely as possible, to get the job done, in a way that kills as many of the bad guys as possible and does as little collateral damage as possible.
"That is just the nature of warfare."