Terrorists detonated a car bomb in southern Baghdad (search) early Wednesday, causing an unspecified number of casualties, witnesses said.

The bomb exploded as a U.S. military convoy was passing in the Dora area of southern Baghdad, witnesses said, adding that Iraqi civilians were injured.

"There was a car bomb but we have no further information as yet," an Iraqi police official said on condition of anonymity.

It was not immediately clear if any American forces were injured in the attack, which happened at around 6:30 a.m.

The U.S. military had no immediate details.

Car and roadside bombs are regularly used by terrorists to strike U.S. and Iraqi forces in Iraq.