Five US Army soldiers were killed by a roadside bomb during Iraq's constitutional referendum, the military said Sunday. It was the deadliest attack against US troops in Iraq since Sept. 29, when five soldiers were killed by a bomb, also in the mostly Sunni Arab city of Ramadi, located 115 kilometers (70 miles) west of Baghdad. Though insurgent attacks were few in most of the country on voting day, Ramadi - a stronghold for insurgents - saw violence. Six mortar rounds hit the Hall of Sports, a facility being used as a voting center, then clashes erupted between gunmen and US troops in the city's center. It was not known if the five soldiers' deaths were connected to this incident. The five soldiers, assigned to the 2nd Brigade Combat Team, 2nd Marine Division, II Marine Expeditionary Force (Forward), were not identified pending notification of their relatives.