The anti-government protesters had feared their campaign would be squashed when riot police on Saturday moved in on their tent camps in the capital, the southern port city of Basra, the holy city of Najaf and other cities.
But the demonstrators returned in large numbers in the evening and on Sunday morning, with security forces trying to clear them out again.
In the capital, they used live rounds in an attempt to disperse small anti-government rallies in Khallani and Wathba squares, near the main protest camp of Tahrir Square, according to a police source.
At least 17 protesters were wounded, including six with bullet wounds, the source said.
The young demonstrators have mostly thrown rocks at riot police but some have tossed Molotov cocktails.
In Nasiriyah to the south, security forces also fired live rounds but there was no immediate word on casualties.
Protesters had gathered there in large numbers after police reopened main thoroughfares in Nasiriyah leading to the central protest camp in Habbubi Square.
The youth-dominated protests erupted in Baghdad and the Shiite-majority south on October 1 in outrage over lack of jobs, poor services and rampant corruption.
Met with violence, they quickly spiralled into calls for a total government overhaul.
Rallies are now specifically demanding snap elections, the appointment of an independent premier and the prosecution of anyone implicated in corruption or the recent bloodshed.
But activists worry they could face a wider crackdown after firebrand cleric Moqtada Sadr dropped his support for the movement on Friday.
The notoriously fickle militia leader-turned-politician backed the protests when they first started and even called on the government to resign.
His supporters had widely been recognised as the most organised and well-stocked protesters in Tahrir.
But after holding an anti-US rally in Baghdad that was attended by thousands, Sadr said he no longer wanted to be involved in the regime change movement.
Within hours, his supporters were dismantling their tents in protest camps across the country and riot police began moving in on demonstrations.
But activists issued an urgent call for help, and young demonstrators flooded Tahrir and other areas.
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