A preliminary military inquiry found evidence that U.S. Marines killed 24 Iraqi civilians in an unprovoked attack in November, contradicting the troops' account of the incident, U.S. officials said Wednesday. President George W. Bush said he was troubled by news stories on the November 19 killings of men, women, and children in the western town of Haditha, and a general at the Pentagon said the incident could complicate the work of the 130,000 U.S. troops in Iraq. "Allegations such as this, regardless of how they are borne out by the facts, can have an effect on the ability of U.S. forces to continue to operate," Army Brigadier General Carter Ham, deputy director for regional operations for the Joint Staff, told a Pentagon briefing. Evidence from corpses showed victims with bullet wounds, despite earlier statements by Marines that civilians were killed by a roadside bomb, a defense official said. "The forensics painted a different story than what the Marines had said," the official told Reuters on condition of anonymity. The official said there were wounds that would not have been caused by an improvised explosive device. "Bad things happened that day, and it appears Marines lied about it," the official said. The incident could represent the worst-known case of misconduct by U.S. troops in Iraq, and comes at a time when opinion polls show falling U.S. public support for the war.