Police say the assailants riding in two cars blocked the bus and opened fire, killing the driver and nine workers. Three other civilians were killed when the bus rammed their car.

Some 170 people have been killed in violence across Iraq in the past week, including at least 14 in a string of attacks Monday

The chairman of the U.S. Joint Chiefs of Staff, General Richard Myers, said Monday the recent wave attacks will not derail the drafting of an Iraqi constitution and the election of a new government later this year.

Iraqi President Jalal Talabani said today the committee working to draft the constitution is making "good progress," and that the document could be ready ahead of the August 15 deadline.