Opposition Web sites and witnesses say Iranian security forces have opened fire on anti-government protesters in the capital, killing at least three people and injuring two others, AP reported.
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.