Voting stations are open across Iraq in places such as military camps and government offices for the first ballots of this week's provincial elections.
The election to choose governing councils in most of Iraq's provinces is scheduled for Saturday.
But special voting began Wednesday for Iraqis needed on duty for election day such as security forces and government officials. Iraqis held in detention also were expected to take part in the early voting.
US and Iraqi authorities hope the election will open the political process to more groups and further erode support for extremist networks. The voting is also being closely watched by Washington as it weighs how fast to withdraw American forces.