Officials sort ballots in Basra, Saturday

Officials in Iraq say there is a possibility that partial results could be released Sunday, but complete ballot counting in Saturday's constitutional referendum is expected to take up to five days.

Election officials said turnout was heavy in at least eight of Iraq's 18 provinces, while another seven provinces reported moderate turnout. Preliminary estimates indicate more than 60 percent of eligible voters cast their ballots.

They were able to cast a yes or no vote on whether to approve the draft constitution.

A simple majority will pass the constitution, but it could fail if two-thirds of voters in at least three provinces reject it.

While some sporadic violence marred the day, Saturday was one of the most peaceful days in Iraq in months. In the day's most serious incident, a roadside bomb killed three Iraqi soldiers.

Iraqi President Jalal Talabani prepares to vote in Baghdad, Saturday

Tens of thousands of Iraqi security forces and police, as well as U.S.-led coalition troops, provided protection for the country's more than 15 million eligible voters as international and local monitors looked on.

There was sporadic violence, but no reports of major insurgent attacks. The only confirmed deaths were of three Iraqi policemen killed by a roadside bomb.

A simple majority of voters is needed to pass the constitution. But it could fail if two-thirds of voters in at least three provinces reject it.

Final results are expected in about three days, but preliminary results could come sooner.