Iraq Prime Minister Adel Abdul Mahdi's two main backers have agreed to work to remove him from office as protests against his government gained momentum in Baghdad and much of the Shia south only to be met with violence.

Populist Shia Muslim leader Muqtada al-Sadr, who leads parliament's largest bloc, had asked Abdul Mahdi to call an early election. When the premier refused, he called on his main political rival Hadi al-Amiri to help remove him.

"I hoping for you to leave with your dignity intact but if you've refused, then I call on Had al-Amiri to help oust you as premier immediately," al-Sadr told the embattled premier and his rival in a Twitter post.

Al-Sadr warned on Wednesday that Iraq could turn into "another Syria" if the government does not resign.

Al-Amiri, who leads a parliamentary alliance of Iran-backed Shia militia that holds the second-largest number of seats in parliament behind al-Sadr's alliance, issued a statement late on Tuesday agreeing to help remove the prime minister. 

"We will work together to secure the interests of the Iraqi people and save the nation in accordance with the public good," al-Amiri said in a statement circulated by Iraqi media. 

Abdul Mahdi took office just a year ago after weeks of political deadlock in which al-Sadr and al-Amiri failed to secure enough votes to form a government. They appointed Abdul Mahdi as a compromise candidate to lead a fragile coalition government.

Amid the spiralling political crisis, Abdul Mahdi has said he could not call an election unilaterally and that parliament must vote with an absolute majority to dissolve itself.

On Tuesday, tens of thousands of Iraqis marched on Baghdad's central Tahrir Square as protests calling for economic reform and removal of the country's political elite continued for a fifth successive day.

The gathering in the Iraqi capital came after an overnight curfew and was the largest of its kind since the eruption last week of a second wave of mass demonstrations this month against official corruption, mass unemployment and failing public services.

The mass protests have been met with a combative response from security forces, who have used tear gas, rubber bullets and live ammunition against those taking to the streets and have been accused by a government-appointed inquiry of using excessive force.

The ongoing turmoil has shattered the nearly two years of relative stability enjoyed in Iraq following the defeat of Islamic State of Iraq and the Levant (ISIL or ISIS).

At least 250 people have been killed since the unrest started on October 1.

Many protesters feel the country's vast oil wealth has not adequately trickled down to its citizens, nearly three-fifths of whom live on less than $6 a day, World Bank figures show.

Millions of Iraqis lack access to adequate healthcare, education, clean water and electricity. Much of the country's infrastructure is in tatters.

Al Jazeera