US military forces killed 11 members of a Mahdi Army splinter group southeast of Baghdad early Thursday, American officials said. It was the largest such operation against the powerful militia in months. It was not immediately clear if the action would impact a six-month freeze on activities that the militia's leader - radical Shi'ite cleric Muqtada al-Sadr - called in August and has signaled in the past week he might extend. Al-Sadr's order to halt activities has been credited by American commanders as one reason why violence in Iraq has fallen dramatically in the past six months. However, it is unclear how much control Sadr maintains over his fighters as groups have splintered from the main movement. Thursday's fighting took place in the early morning hours in Kut, 160 kilometers (100 miles) southeast of Baghdad, a local police officer said on condition of anonymity because he was not authorized to speak to the press. The officer said eight militia members were killed; the US military said that it killed an "estimated" 11 fighters. The reason for the discrepancy was not immediately clear. In a later statement, the US military said the operation was targeting a suspect who was "reportedly responsible for attacks against Coalition forces." Troops approaching the target were fired at with assault rifles and rocket propelled grenade, the military said. They then called in support aircraft. The local police official said at least two US helicopters were used in the attack, along with an unknown number of fighter jets. No US troops were killed or wounded in the operation, the military said. Despite its freeze on activities, US commanders have in the past said they would not stop targeting splinter elements of the Mahdi Army that they said continue to operate, in violation of Sadr's order.