Iran's semi-official Mehr news agency is reporting a gunman has killed one policeman and wounded three other officers during a protest gathering.
Without elaboration the late Monday report says the assailant used a hunting rifle to shoot the policeman in the central city of Najafabad, some 320 kilometres (200 miles) south of Iran's capital, Tehran.
This is the first report of a police officer being killed during five days of protests and raises the total number of dead to 13.
Earlier on Monday, Iranian state TV said 12 people had been killed amid the nationwide protests. The report said that included 10 deaths during clashes Sunday night when security forces repelled what officials described as "armed protesters'' trying to take over police stations and military bases.