BAGHDAD, Aug 23 (Reuters) - Nine Iraqi policemen in Baghdad have been detained by U.S. forces on suspicion of involvement in a roadside bomb attack near a police checkpoint, the U.S. military said on Thursday. The policemen were detained during a security sweep in Baghdad's notoriously dangerous southern Rashid district on Tuesday and were being held for questioning, the military said. The Iraqi police are widely viewed as deeply infiltrated by Shi'ite militias, which are blamed for attacks on U.S. troops and members of Iraq's minority Sunni Arab community. U.S. soldiers have voiced suspicions in the past that Iraqi police are involved in some of the roadside bomb attacks because they occur so close to police checkpoints. Military commanders are also concerned about the performance of the police, who are seen as poorly trained and led and riven with sectarianism.