U.S. military officials say a mortar attack killed one Iraqi and injured 12 others late Wednesday at a coalition-run aid office north of Baghdad. This is one of several recent attacks against Iraqis working with coalition forces.

A U.S. military statement says a mortar was fired at the Civil Military Operations center in the town of Samarra. The center is a coalition-run office that coordinates humanitarian assistance between the military and civilian, non-governmental agencies.

In another incident earlier this week, gunmen fired at the mayor's office and courthouse in the town of Fallujah, west of Baghdad, and at a police station in Khaldiyah.

There have also been almost daily attacks or ambushes against U.S. troops.

One U.S. soldier was killed and another injured in an attack at a gas distribution center Wednesday in central Baghdad. More than 40 U.S. troops have been killed in such attacks since May 1.

The coalition blames elements loyal to Saddam Hussein and a major nationwide operation is under way to root out these armed groups.

Military officials announced Wednesday they had captured the number-four man on the U.S. most wanted list, Saddam Hussein's top aide and bodyguard, Abid Hamid Mahmoud al-Tikriti. Officials believe he may know the fate or possible whereabouts of the deposed Iraqi leader.

While the coalition says remaining elements of the old regime are behind the attacks, some Iraqis say public anger is fueling resentment against the American troops.

Iraqis accuse U.S. forces of heavy-handed tactics in their search for banned weapons and suspected Saddam loyalists.