A hundred thousand Iraqis across the country marched today in support of a maverick Shi'ite cleric opposed to a draft constitution.
The protest could reinforce the opposition of Sunni Arabs who dominate the insurgency and are bitterly against the draft.
Supporters of Moqtada al-Sadr, who has staged two uprisings against US troops, also protested against poor services during their marches, stepping up the pressure on the government.
A hundred thousand Sadr supporters marched in eight cities, including 30,000 people who gathered for a sermon delivered on his behalf in a Baghdad slum district.
Sadr returned to centre stage this week after his fighters fought a rival Shi'ite militia, the Badr organization, raising fears of a new front in Iraq's relentless cycle of violence.
He is stirring hopes among his vast following at a time when Iraq's divided politicians have missed a series of deadlines for reaching a consensus on the constitution, which is expected to be put to a referendum in October.
Sadr has also come out in support of Sunni opposition to the federal state that his Shi'ite rivals in government, with their Kurdish allies, have outlined in the charter.
"Bush and America out," yelled cleric Abdel-Zahra al-Suwaidid, reading a statement on Sadr's behalf in the Baghdad slum of Sadr City which is named after his revered father, a cleric allegedly killed by Saddam Hussein's agents.
Another widespread complaint was written simply on banners: "We want water, we want electricity."
The young cleric has gained followers by portraying himself as a champion of the poor. Sadr's cult-like popularity means he can quickly mobilize his fighters if a full-scale conflict with the Badr movement breaks out.
Sadr, who has denied US and Iraqi government accusations he ordered the killing of a rival cleric, assumed a low profile after a U.S. offensive against his forces last year in Najaf.
Now he faces the Iranian-trained Badr movement, which some Iraqis accuse of operating in hit squads alongside government forces. Badr officials and the government deny the accusations.
Sadr's supporters say Badr militiamen attacked his office in Najaf on Wednesday, and clashes then erupted in several cities. A Badr official denied any involvement. Eight people were killed, health officials said.
The fighting between the two groups across several cities raised the spectre of a new security crisis in Iraq, already ravaged by a Sunni Arab insurgency that has killed thousands of Iraqi police and soldiers, civilians and US troops.
At the Baghdad protest, fighters in Sadr's Mehdi Army stood alert on rooftops with assault rifles as speakers condemned the United States.