Thousands of supporters of Shia militia leader Moqtada Sadr, who was reported wounded on Friday in the besieged city of Najaf, marched through Baghdad, saying they were willing to die as his martyrs.
Demonstrations also took place in other places, including Tallafar, northwest of the main northern city of Mosul, Kut and Kut al-Hayy south of the capital, and Kufa near Najaf.
The crowd set out from the cleric's Baghdad bastion of Sadr City, in the northeast of the capital, for the heavily fortified Green Zone, which houses some government offices.
"We want to be martyrs for you, Moqtada Sadr" and "He's the bridge to paradise," the men chanted as they walked and drove through the centre of the city packed into buses, trucks and cars, an AFP correspondent said.
The men, none of them armed, denounced Iraqi Prime Minister Iyad Allawi, who has pressed Sadr's Mehdi Army to surrender after more than a week of fierce fighting against US troops and Iraqi forces in the holy city of Najaf.
"We want to hold a peaceful demonstration outside the convention centre" inside the Green Zone, said one of the protesters, who refused to give his name.
The men held aloft a sea of flags and carried banners reading "Shoot Down American Planes" and "Leave Moqtada Sadr".
At one point along the route, police were called out to defuse a multiple car bomb that would have caused carnage had it detonated.
"We found six missiles connected and ready to explode. A major tragedy was diverted because there were hundreds of protesters passing along the road," said police Lieutenant Mohammed Jassem.
In Tallafar about 300 demonstrators took to the streets of the mainly Shiite town, calling on Allawi and the interior and defence ministers to resign, along with the Najaf governor.
"Residents of Tallafar promise to be Moqtada Sadr's soldiers in fighting the Americans," they chanted, calling on the premier and his "failure" government to step down.
In the small town of Kut al-Hayy, more than 1,000 people from all backgrounds marched through the streets after Friday prayers to demand an end to bloodletting.
Sadr's local representative, Ashraf al-Husseini, called for an immediate end of the foreign occupation of Iraq and for the assault in Najaf to stop, as protesters held up a banner calling for the dismissal of the defence, interior and prime ministers.
In Kufa, thousands of Sadr supporters were marching towards Najaf in support of Sadr, an AFP correspondent said.
In the city of Kut, where suspected Sadr militia strongholds have been pounded by two US attacks in 24 hours, residents donated food and essential supplies for the people of Najaf.