Protesters blocked roads with burning tyres in southern Iraq and clashed with police in Baghdad on Wednesday, aiming to use economic disruption as leverage to push the government from power and root out state corruption.

Security forces shot dead two people in Kerbala overnight and two in Baghdad on Wednesday, while a fifth person died from gunfire by security forces during protests in the southern oil capital of Basra.

Demonstrators prevented government employees from getting to work in Basra by installing concrete barriers painted as mock-up coffins of relatives killed in weeks of unrest, a Reuters witness said.

Iraq's large protests are the most complex challenge to a Shia Muslim-dominated ruling class that has controlled state institutions and patronage networks since a 2003 US-led invasion toppled Sunni dictator Saddam Hussein.

Young, mostly Shia protesters say politicians are corrupt and blame them for Iraq's failure to recover from decades of conflict and sanctions despite two years of relative calm following the defeat of the militant Islamic State group.

The unrest has shattered that calm and authorities warn against its exploitation by armed groups, especially should protest-related violence spread to northern Iraq where IS militants are waging an insurgency.

The extremist group on Thursday claimed three bomb blasts in Baghdad overnight which killed at least six people but provided no evidence for the claim.

Government reform has amounted to little more than a handful of state jobs for graduates, stipends for the poor and pledges of election reform which lawmakers have barely begun to discuss.

“First we were demanding reform and an end to corruption,” said Ali Nasser, an unemployed engineering graduate protesting in Basra.

“But after the government started killing peaceful protesters we won't leave before it's been toppled together with the corrupt ruling class.”

Slow, meaningless reform

Alia, a 23-year-old medical student, said: “The reforms are just words. We want actions. We've had 16 years of words without actions. We have been robbed for 16 years.”

Security forces meanwhile shot dead more demonstrators. In the holy city of Kerbala, south of Baghdad, they used live ammunition against protesters, killing two overnight. Two more were killed in clashes near Baghdad's Ahrar Bridge on Wednesday.

Near Basra one protester died of wounds from gunfire, police and medics said, bringing the toll since unrest broke out on October 1 to 344 people dead nationwide.

Prime Minister Adel Abdul Mahdi expressed concern over both the violence and the financial toll of unrest late on Tuesday, but mostly blamed unidentified saboteurs for the damage.

“There have been martyrs among protesters and security forces, many wounded and arrested ... we're trying to identify mistakes” made by security forces in trying to put down the protests, he told a televised cabinet meeting.

“The blocking of ports has cost billions of dollars.”

Protesters have blocked traffic into Iraq's main commodities port near Basra this month and tried to surround the Central Bank in Baghdad, apparently bent on causing economic disruption where calls for removal of the government have failed.

The government is moving slowly in enacting any kind of change. Promises of electoral reform and an early general election have yet to be ratified by parliament, and the political class has closed ranks in the face of a significant challenge to its grip on power.