All four of the soldiers killed in a bomb attack in southern Afghanistan were Americans, a Pentagon official said Monday. The NATO international military command in Kabul provided no details on Monday's attack, including the nationalities of the dead. But in Washington, a defense official told the Associated Press on condition of anonymity that the victims were American and were hit by an improvised explosive device (IED). The latest fatalities make a total of 16 NATO troops killed so far this month and 167 so far this year.