(Reuters) - The dust had barely settled from the last column of departing U.S. armoured vehicles when Iraq's rival Sunni and Shi'ite factions resumed the kind of political infighting that threatens a lurch back into turmoil.

Within hours of the last U.S. troops rolling out of Iraq on Sunday, Shi'ite Prime Minister Nuri al-Maliki had asked parliament to sack his Sunni deputy, and security sources said an arrest warrant was issued for the Sunni vice president.