"Shiite Muslim militias pose the greatest threat to security in many parts of Iraq, having killed more people in recent months than the Sunni Arab-led insurgency, and will likely present the most daunting and critical challenge for Iraq's new government, U.S. military and diplomatic officials say." (Notice that this Washington Post's article does not mention US troops. US troops don't kill in Iraq; only Sunnis and Shi`ites do, according to the Post).