An Iranian opposition website said another pro-reform protester was killed in Tehran during clashes with police, near the area where it earlier reported three demonstrators were killed on Sunday.
Seperately, witnesses said the mobile phone network in Tehran appeared not to be working.
"Protesters chanted anti-governemnt slogans when carrying his body," the Jaras website reported.
Earlier Sunday, opposition websites and witnesses said Iranian security forces have opened fire on anti-government protesters in the capital Tehran.
Authorities had warned of a harsh crackdown should opposition supporters hold rallies coinciding with Sunday's religious observances marking the 7th Century death in battle of one of Shiite Islam's most beloved saints.
Police helicopters circled overhead and clouds of smoke billowed into the sky.
The pro-reform Web site Rah-e-Sabz said security forces fired on protesters, killing at least three.
Witnesses say one of the victims was an elderly man who had a gunshot wound to the forehead. He was seen being carried by opposition supporters.