So far, military officials say they have made no decisions on future troop withdrawals. They say they are sticking to current plans to send additional units to Iraq later this summer, and acknowledge that a decision will have to be made soon on whether to keep some of those troops home instead.

One Defence Department official said the military is waiting to see if attacks between the majority Shia Muslims and the Sunni Arabs escalate or slack off. Military units will continue preparing to go to Iraq because it is easier to cancel deployment orders than to restart preparations if troops are suddenly needed, said the official, who requested anonymity because troop decisions have not been finalised.

Maj. Gen. Rick Lynch, a military spokesman in Baghdad, played down suggestions the fragile country is on the brink of civil war. He said Thursday there is a sense that this may just be another peak in the violence in Iraq, and it may not continue at the level seen in recent days.