The country has been rocked by the biggest wave of protests since the 2003 US-led invasion toppled Saddam Hussein, leaving more than 350 people dead and around 15,000 wounded since early October.

Violence had erupted in the southern holy city of Karbala on Tuesday, with one protester killed as riot police fired live rounds both into the air and directly into crowds of teenagers pelting them with rocks.

Fearing more bloodshed, Karbala's religious authorities ordered their network of private schools in the city, as well as in nearby Babylon and the second holy city of Najaf, kept shut for two days starting Wednesday.

Thick columns of black smoke could still be seen rising from Karbala, which is visited every year by millions of Shiite pilgrims from around the world, as demonstrators torched tyres around and inside the city.

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

Iraq's street violence has left many thousands wounded.

Another 100 protesters suffered injuries in two days of rallies in Al-Hillah, just south of Baghdad, when security forces began using tear gas against protesters.

In the protest hot spots of Diwaniyah, Kut and Najaf, activists also cut roads with flaming tyres to keep government employees from reaching their offices.

And outside the oil-rich port city of Basra, picketers sealed off the entrance to the Nasiriyah oil field, a contributor to Iraq's exports of some 3.6 million bpd.

The country is OPEC's second-largest crude producer, and oil exports fund more than 90 percent of the government's budget.

The industry has so far remained relatively insulated from the widespread protests.

In central Baghdad, where at least one protester was killed Tuesday, young demonstrators donned helmets and medical masks to again face off with security forces who were unleashing tear gas on them.

A major flashpoint has been the historic Rasheed Street and its nearby colonnaded alleys, where riot police has clashed with demonstrators.

Police have sought to keep the protesters from reaching the nearby Al-Ahrar bridge across the river Tigris that leads to key government buildings on the western side.

Late Tuesday, Baghdad was rocked by another kind of violence -- three explosions that went off just after Iraqis had celebrated a football win against Qatar in the Gulf Cup.

Six people were killed in the near-simultaneous blasts from explosives-laden motorcycles and roadside bombs in several Shiite neighbourhoods, according to medical and security sources.

They were the first such blasts in Baghdad in several months, but there was no immediate claim of responsibility.