Iranian media say authorities believe Kurdish rebels are behind the shooting death of a local prosecutor.
Attackers shot Vali Haji Gholizadeh late Monday outside his home in the town of Khoy in northwestern Iran.
Authorities have detained four suspects.
The Iranian news agency ISNA quotes a provincial official as saying no one has claimed responsibility for the killing. But Mohammad Ali Mousavi, who heads the region's justice department, says he suspects the Kurdish separatist group, Party of Free Life in Kurdistan, or PJAK. Mousavi said the group had threatened the prosecutor in recent days.
The Kurdish rebel group is linked to Turkey's outlawed Kurdistan Workers Party, or PKK.
Iran has been fighting separatist rebels in its Kurdish-populated areas for the past few years.
The French news agency, AFP, initially quoted an Iranian interior official, Fakhrali Nikbakht, as saying the PJAK had claimed responsibility. But Iranian media quoted other government officials who said no group had claimed responsibility for the attack.
The attack on the prosecutor came nearly a week after a Tehran University physicist was killed by a remote-controlled bomb in front of his home in the Iranian capital. No group has claimed responsibility for that assassination and no arrests have been made.
Some information for this report was provided by AP, AFP and Reuters.