Pentagon officials acknowledged Tuesday that US troops used white phosphorous as a weapon against insurgent strongholds during the battle of Fallujah last November. At the same time, they denied an Italian television news report that the spontaneously flammable material had been used against civilians. Lt. Col. Barry Venable, a Pentagon spokesman, said that while white phosphorous is used most frequently to mark targets or obscure positions, it was used at times in Fallujah as an incendiary weapon against enemy combatants. "It was not used against civilians," Venable said. The State Department initially denied that US troops had used white phosphorous against enemy forces. "They were fired into the air to illuminate enemy positions at night, not at enemy fighters," a department Web site said. The department later said the statement had been incorrect. Venable said white phosphorous shells are a standard weapon used by field artillery units and are not banned by any international weapons convention to which the US is a signatory.