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 al-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.