One US contractor was hit by shrapnel but not injured.
He was also accused of participating in the kidnapping of three US contractors.
In total, 4,800 military personnel, 840 German nationals and 200 US contractors are working at the base.
U.S. contractors will be subject to Iraqi criminal law.
We had local offices in a tough environment where traditional U.S. contractors would not operate.
They were dragged from their car in one of the most violent attacks on U.S. contractors in the conflict.
Like many U.S. contractors, Boeing is rebuilding weapons instead of making more expensive new ones.
"Our assumption is that some of the training may be done through contractors, which would not exclude U.S. contractors."
Saudi Arabia is nearing agreement with five big U.S. military contractors to stretch out $10 billion in payments.
According to Airbus, US contractors, supporting an estimated 120,000 jobs, earned an estimated $5.5 billion (2003) worth of business.