Three protesters were shot dead in Iraq on Saturday in clashes with security forces clearing out streets and squares occupied for months by anti-government demonstrators, stoking fears of a wider crackdown.

The fresh violence came a day after populist cleric Moqtada Sadr announced he would no longer back the youth-dominated movement, instead holding his own rally in Baghdad to demand US troops leave Iraq.

Protesters feared the withdrawal of his support could pave the way for authorities to suppress their movement and by Saturday evening, clashes had broken out between riot police and demonstrators across Iraq.

In the southern flashpoint of Nasiriyah, two protesters were shot dead and some 20 wounded. Another demonstrator was shot dead and more than 40 were wounded in skirmishes in Baghdad, a medical source said.

Since early Saturday morning, security forces had been using tear gas and live rounds to clear protest camps in the capital, with an AFP reporter seeing some wielding batons chase a group of young protesters. A medic told AFP she saw riot police set fire to large tents used as field clinics to treat wounded demonstrators.