An Iraqi parliamentary candidate was shot dead late on Sunday in his home near the city of Mosul, a family member and a security official said, less than a week before elections.
Islamic State claimed responsibility for the shooting of Farouk Zarzour in the village of al-Lazaka, but security officials disputed that claim and said they were treating it as a political killing.
Zarzour's brother and eight others have been arrested as suspects, they said.
Zarzour had been an adviser to parliamentary speaker Salim al-Jabouri.
The Islamic State militants have threatened to carry out attacks ahead of the elections and have warned Sunni Arabs not to participate. However, the hardline militants have also claimed responsibility for several attacks that never happened.
Iraqi Prime Minister Haider al-Abadi declared nationwide victory over the Islamic State in December, five months after his forces recaptured Iraq's second city Mosul in a protracted battle with the jihadist militants.
Islamic State, however, continues to carry out bombings, assassinations and ambushes in different areas of Iraq, and remains active in neighbouring Syria.