A spokesman for the U.S. military has admitted that soldiers used white phosphorus as an "incendiary weapon" while trying to flush out insurgents in the northern Iraqi city of Fallujah last year.

"White phosphorus is a conventional munition," Lt.-Col. Barry Venable told the British Broadcasting Corporation. "It is not a chemical weapon. They are not outlawed or illegal."

He added that though used mostly to provide smokescreens and flashes of light, in the Fallujah battle, "it was used as an incendiary weapon against enemy combatants."

High-ranking U.S. officials had earlier insisted that the substance, which can burn skin to the bone, was used only to help illuminate battle scenes.

"U.S. forces do not use napalm or white phosphorus as weapons," the American ambassador to London, Robert Tuttle, wrote in a letter to the Independent newspaper.

An unknown number of Iraqi women and children died of phosphorus burns during the hostilities, Italian documentary makers covering the battle for Fallujah have claimed.

Other reporters on the scene have said U.S. forces used a combination of white phosphorus and explosives known as "shake 'n' bake."

Venable's comments could expose the United States to allegations that it has been using chemical weapons in Iraq.

The suspicion that former president Saddam Hussein was developing chemical weapons, as well as biological and nuclear ones, was one of the Bush administration's main justifications for the 2003 invasion of the Persian Gulf country.