Gunmen ambushed a car carrying American civilians on a road south of Baghdad, killing one and wounding three others, the US military said.
The attackers, driving a white sedan, opened fire on the taxi that the Americans were taking to Baghdad from the site of the ancient city of Babylon, the survivors told US troops, a statement from the military said.
US paratroopers learned of the attack on Saturday while conducting a patrol in the town of Mahmudiyah, about 15 miles south of Baghdad, and were told the Americans were being treated at hospital there.
The statement said the Americans were part of a "religious group" but did not identify it. There are a number of Christian humanitarian groups working in Iraq.
Insurgents have been waging a campaign of attacks on US troops and their Iraqi allies and have occasionally targeted aid workers.
A US soldier was killed and another wounded today when their convoy was hit by a roadside bomb in central Baghdad, a US military spokesman
said.
The death brought to at least 374 the number of US soldiers killed in combat since the invasion of Iraq in March.