The attack took place in a popular restaurant in Khanaqin, a town bordering the semi-autonomous Kurdistan region in northern Iraq.
The town has been a source of friction between Kurds and the Arab-run central government.
Hundreds of Kurds complained on election day that they couldn't find their names on voter registration lists.
Election results announced on Thursday show that the Dawa party led by Nuri al-Maliki, Iraq's prime minister, has won in Baghdad and eight other provinces.
That strong showing would give al-Maliki - once seen as a weak leader installed by more powerful Shia parties - his own power base in the provinces and strengthen his hand ahead of the national elections.