5 U.S. soldiers killed in Baghdad ambush

The boycotts are likely to complicate efforts to enact key "benchmark" legislation that the U.S. is demanding, since the Cabinet must sign off on such proposals before they go to parliament.

Even if the other Shiite and Kurdish members give their endorsement, the absence of key constituencies from the decision-making process would raise doubts whether such legislation would contribute to the goal of national reconciliation.

Elsewhere Friday, a suicide truck bomber attacked an Iraqi army post 20 miles north of the capital Friday, killing six soldiers and wounding five others, police said. Two civilians were also killed in a barrage of gunfire that followed, they said.

The blast occurred at a railway station in Mishada, an officer said on condition of anonymity because he was not authorized to release the information.

Iraqi police said a bomb exploded under a pipeline south of Baghdad, spilling crude oil and sparking a huge fire. The pipeline carries oil from Iraq's southern oil fields to the Dora refinery in the capital.