text: 6 U.S. Soldiers Killed in Iraq Attacks BAGHDAD, Iraq - A suicide attack and roadside bombings killed six American soldiers, and Iraq's prime minister warned residents of insurgent bastion Fallujah on Wednesday to hand over terror mastermind Abu Musab al-Zarqawi or face military action.    Al-Zarqawi's Tawhid and Jihad group has claimed responsibility for beheading several foreign hostages and for car bombings throughout the country, and a videotape posted Wednesday on an Islamic Web site showed militants linked to al-Zarqawi beheading two Iraqis they accused of being intelligence officers...