Two senior police officials have told the Associated Press that gunmen arrived at an military base in the town of Udaim at dawn in three vehicles and began shooting at soldiers.
The officials spoke to the media on condition of anonymity.
Gunmen have killed 13 soldiers at an Iraqi base taking the death toll in the country to 82 - the bloodiest day of the year, according to the Associated Press.
The number killed in a wave of explosions across Iraq has risen to at least 69.
A wave of bomb attacks in Iraq has killed at least 51 people, according to the Associated Press.
A car bomb outside a Baghdad office issuing government ID cards killed 14 people and earlier attacks in the town of Taji, just north of the capital, left 28 dead.
Blasts in the oil city of Kirkuk killed another nine people.
A string of explosions in Iraq, including a car bomb and suicide attack in the capital Baghdad and four car bombs in the northern oil city of Kirkuk, have killed 39 people and injured at least 118.
The death toll from a wave of bomb attacks in Iraq has risen to at least 39, police and hospital sources have told Reuters.
A wave of bomb attacks in Iraq has killed at least 28 people, according to the Associated Press.
After initial explosions, a suicide bomber targeted Iraqi policemen rushing to help, the news agency added.