The anti-government demonstrators attempted to bloc the path of a rally supporting Shiite Muslim leader Moqtada al-Sadr. Followers of the populist cleric also wounded 40 others in the clashes, according to two medical officials.
The officials spoke on condition of anonymity in line with regulations.
The anti-government protesters were camped out at a main square in the city of Nasiriya, which has been an epicenter of the youth-led protest movement that has sought to sweep aside Iraq's ruling sectarian elite.
Following the clashes beginning on Friday, al-Sadr’s supporters stormed Haboubi square, and torched tents pitched in the square.
Anti-government protesters feel betrayed by al-Sadr’s flip-flop approach toward them, especially in the last few months when he withdrew support for their movement.
Dozens returned to the anti-government sit-in's site on Saturday morning in support of those protesters killed overnight.