File Photo - Fighters from the Islamic State group parade in a commandeered Iraqi security forces armored vehicle in the northern city of Mosul, Iraq on June 23, 2014. AP
The violence, in Diyala province, occurred on Thursday evening and targeted a minibus returning the civilians from an electoral meeting organised by a candidate from their tribe, an interior ministry official, who asked for anonymity, told AFP.
Muthana al-Tamimi, the governor of Diyala which is just outside Baghdad, denounced "a cowardly operation" by Islamic State (IS) group jihadists.
On his Facebook page he called on the security forces to "intensify vigilance against dormant cells" of the extremists.
IS did not immediately claim the attack in Diyala, an area where its cells remain active.
In the Diyala unrest, at least "11 people were killed and 17 wounded in an attack carried out by an explosive device then gunfire targeting the gathering" provoked by the initial blast in Al-Omraniya village, said a second security source in Baghdad.
The interior ministry source said the minibus was targeted "by two homemade bombs on its return from an electoral meeting".
Sniper fire followed, according to this source, who gave a toll of 12 civilians dead and 13 wounded.
The attack came ahead of the election on December 18 of provincial councils, which in turn elect the governors.
About 2,500 US troops remain in Iraq as part of international efforts to prevent a resurgence of IS.
A United Nations report published in July said IS has "between 5,000 and 7,000 members across Iraq and the Syrian Arab Republic, most of whom are fighters".