BAGHDAD, Iraq -- Shiite clerics joined Sunni preachers in a march of thousands of mostly black-clad men Wednesday, trying to keep sectarian passions in check after a horrific attack on Shiite pilgrims that raised fears of civil war.

U.S. and Iraqi officials disagreed over how many people died in Tuesday's bombings in Baghdad and Karbala the deadliest since the fall of Saddam Hussein. The Iraqi Governing Council said 271 people were killed. U.S. officials put the toll at 117.