Masked youths sealed off streets with makeshift barricades across the restive south as schools and public offices stayed shut.

"The government has lost all its legitimacy. We don't want them," said one protester in the southern city of Basra.

"They meet every day and claim to be discussing our demands, but we expect nothing from them."

For nearly two months, Iraq's capital and Shiite-majority south have been gripped by the largest protests since the 2003 US-led invasion that toppled Saddam Hussein.

In central Baghdad, young demonstrators donned helmets and medical masks to face off again with security forces unleashing tear gas.

Iraqi medical and security sources said at least two demonstrators were shot dead in Baghdad as protesters and security forces clashed.

An AFP correspondent reported volleys of gunfire from behind concrete barricades where the security forces were deployed.

The Islamic State group, meanwhile, claimed that it was behind three deadly explosions that rocked Baghdad late on Tuesday, killing six people.

The near-simultaneous blasts were caused by explosives-laden motorcycles and roadside bombs in Shiite neighbourhoods, medical and security sources said.

They were the first such attacks in Baghdad in several months claimed by IS, a group which the Iraqi authorities said had been defeated two years ago.

- Daily life paralysed -

The street violence in Iraq has left more than 350 people dead and some 15,000 wounded over the past two months.

Another 100 protesters suffered injuries in two days of rallies in Hillah, just south of Baghdad, when security forces used tear gas against them.

The unrest has paralysed daily life in many towns and cities, with schools intermittently closed, streets blockaded and government offices empty.

On Wednesday, religious authorities in the holy city of Karbala ordered their private schools there, and in nearby Babylon and the second holy city of Najaf, kept shut for two days.

They feared a repeat of Tuesday's chaos when riot police and protesters clashed, leaving one demonstrator dead.

Karbala, visited by millions of Shiite pilgrims from around the world each year, had seen deadly skirmishes overnight and during the day.

Demonstrators on Wednesday torched tyres in and around the city, sending thick plumes of black smoke barrelling skywards.

In Nasiriyah, further south, authorities ordered all public offices closed for two days, although these had been largely shut already by ongoing sit-ins and marches.

- 'Chaos and corruption' -

Activists also cut roads with flaming tyres in protest hot spots Kut and Najaf, keeping government employees from going to work by staging sit-ins.

In Diwaniyah and the oil-rich port city of Basra, no security forces could be seen as demonstrators hit the squares and streets.

Picketers also sealed off the entrance to the Nasiriyah oilfield, a contributor to Iraq's exports of some 3.6 million barrels per day.

The country is OPEC's second-largest crude producer and the oil exported through Basra's offshore terminals funds more than 90 percent of the government's budget.

The industry has so far remained relatively insulated from the unrest, but Basra residents are seething over notoriously poor water provision, an unstable electricity supply and sub-par public schools.

"It's been 16 years that we've been living in chaos and corruption," one protester told AFP on Wednesday.

"Basra should have been a wealthy city, but instead it's a trash dump."

Corruption is rampant in Iraq, ranked the world's 12th most graft-ridden country by Transparency International.

A government probe found that $450 billion in public funds had been lost to graft, fake contracts and so-called ghost employees since 2003.

One in five Iraqis lives in poverty and youth unemployment stands at 25 percent, according to the World Bank.