Iraqi security forces clashed with protesters in Baghdad, Nasiriyah and Basra on Saturday after authorities began to remove concrete barriers near anti-government demonstration sites.
Dozens of protesters were wounded in clashes with police and at least three protesters were shot dead.
Authorities advanced toward Tahrir Square in Baghdad, where the main protest camp is based, shooting live rounds and firing tear gas in an effort to disperse protesters.
The Baghdad Operations Command said security forces also reopened Mohamed al-Qassim highway and other roads near Tahrir Square.
Protesters' tents were also reportedly set alight as police tried to remove them in order to reopen public squares and at least one bridge over the Tigris River.
Demonstrators fear that their long-running campaign would be sidelined if they were cleared from the site at Tahrir Square.
Sadr withdraws support
The fresh clashes happened a day after populist Shiite politician and cleric Muqtada al-Sadr organized his own mass rally demanding US troops leave Iraq, before announcing that he would no longer back the protest movement.
In a tweet Friday evening, Sadr indicated his "disappointment" toward anti-government protesters in Baghdad.
The removal of his support is a heavy blow to the tens of thousands of protesters, many of them from Baghdad's slums, who have taken to the streets and who saw Sadr as a leader.
Basra camp also raided
Security officials also stormed a large protest camp in the port city of Basra, forcing activists to flee. They arrested 16 sit-in protesters.
There are concerns that security forces are aiming for a wider crackdown to end months of unrest, taking advantage of Sadr's removal of support for the activists.
Some 470 people have been killed since the protests erupted in the capital and the Shiite-majority south in October.
The protests were initially fueled by anger over graft and joblessness but then ballooned into demands for deep political reforms.
ed/mm (Reuters, AP, AFP, dpa)