In Baghdad, crowds of anti-government demonstrators thronged Tahrir Square, the epicentre of their movement.

Late Friday, unidentified gunmen attacked a parking complex near Tahrir where demonstrators had been squatting for weeks, leaving 20 protesters and four police officers dead, medics told AFP.

Protesters feared it signalled that their movement would be derailed but by Sunday, the numbers gathered under the sun in Tahrir were staggering.

"They're trying to scare us in whatever ways they can, but we're staying in the streets," said Aisha, a 23-year-old protester.

At least 452 people -- the vast majority of them protesters -- have died and 20,000 have been wounded since the rallies erupted.

In Nasiriyah, a protest hotspot where dozens were killed in a spree of violence last month, protesters regrouped in downtown along with representatives of powerful tribes.

"We will keep protesting until the regime collapses," pledged Ali Rahim, a student.

In other southern cities, local authorities had declared Sunday -- the first day of the work week in Iraq -- a holiday for civil servants.

Road blocks and massive strikes also disrupted work in Hilla, Amara, Diwaniya, Kut and the shrine city of Najaf, AFP's correspondents there said.

The rallies have persisted despite the resignation of premier Adel Abdel Mahdi earlier this month, with protesters demanding the complete ouster of the ruling class.

Iraq is ranked the 12th most corrupt country in the world by watchdog group Transparency International, with billions of dollars pilfered each year from the state budget of OPEC's second-largest producer.