BAGHDAD, Iraq - Iraqi police said a car bomb killed up to 18 boys on a soccer field Tuesday, but a spokesman for the U.S. military later said the explosion was a controlled blast by American soldiers and that 30 people, including nine children, were slightly wounded. The blast occurred in Ramadi, a hotbed of the Sunni insurgency. Maj. Jeff Pool, a Marine spokesman in Iraq, said the U.S. military was unaware of the attack described by Iraqi officials. "I can't imagine there would be another attack involving children without our people knowing," he said.