Security forces used water cannons and tear gas to disperse thousands of angry protesters in Baghdad on Friday as a "Day of Rage" across Iraq left 15 demonstrators dead in clashes with police.

Around 5,000 people thronged Baghdad's Tahrir Square, with angry crowds throwing stones, shoes and plastic bottles at riot police and soldiers blocking off a bridge connecting the site to Baghdad's heavily fortified Green Zone, home to the US embassy and parliament.

The protest was the biggest of at least 17 separate demonstrations across the country, some sparking clashes in which more than 130 people were wounded, according to an AFP tally based on accounts by officials.

Four government buildings were also set ablaze and one provincial governor resigned.

By evening, most of the crowd in Baghdad had left and security forces refused to allow anyone to enter the area surrounding the square.

An AFP journalist said security forces had used a water cannon and tear gas in a bid to disperse the crowd. An interior ministry official said 15 people were wounded.

During the protest, demonstrators overturned two concrete blast walls on Jumhuriyah bridge, spurring lines of anti-riot police and soldiers to block it off.

Security was deployed in force, imposing a city-wide vehicle ban after Prime Minister Nuri al-Maliki claimed Al-Qaeda insurgents and loyalists of deposed dictator Saddam Hussein were behind the demonstrations.

The vehicle curfew, initially put in place overnight, had not been lifted by security forces in the capital by late on Friday.

After the Baghdad protests ended, Maliki said in a statement that Iraqis behaved responsibly, and that the country "did not give a chance to terrorists to take action."

Rallies in Iraq have called for improved public services, more jobs and less corruption, and some for broader political reforms.

Rated the fourth-most corrupt country in the world by Transparency International, Iraq suffers from poor electricity and water provision, as well as high unemployment nearly eight years after the 2003 US-led invasion.

MP Sabah al-Saadi, who turned up at the Baghdad protest, was met with shouts and jeers, with one protester asking: "Why are MPs taking millions of dinars (thousands of dollars) in salaries?"

"You have to cut your salary -- we have nothing! Why are you taking so much money when we have no money?"

But attendance at the Baghdad protest, which had been expected to draw tens of thousands, was partly muted by the fact that several religious leaders asked their followers not to attend.

Radical Shiite cleric Moqtada al-Sadr, in particular, said his partisans should give the government, of which his bloc is a key member, six months to improve its record.

Friday's rally, like others across the region, was largely organised on social networking website Facebook and billed as Iraq's "Day of Rage," in reference to events in Egypt that forced out president Hosni Mubarak.

Mostly young men gathered in Tahrir Square, which shares the name of the square in Cairo where Egyptians rallied to overthrow Mubarak.

"It is now eight years, and they have done nothing for us. Stop the words, we want action!" said Ammar Raad, 33.

Press watchdog Reporters Without Borders criticised the vehicle ban, saying television channels would not be able to park their satellite trucks near the protests and thus were unable to broadcast live.

A cousin of Muntazer al-Zaidi, who shot to fame for hurling shoes at then US president George W. Bush in 2008, told AFP the reporter had been detained by security forces since Thursday after arriving to join the protests.

Elsewhere in Iraq, vehicle curfews were slapped on the central cities of Samarra, Tikrit, Baquba, and the western city of Ramadi.

North of Baghdad, clashes between security forces and demonstrators in the cities of Mosul and Tikrit each left five people dead, while two others died in the northern town of Hawija.

Two other demonstrators were killed in Samarra, while a 15-year-old boy died in the mostly Kurdish town of Kalar in central Diyala province.

Protesters set fire to provincial government offices in Mosul and the city council building in Hawija, as well as two official buildings in Fallujah, west of Baghdad.

In the port city of Basra, the provincial governor resigned after 3,000 protesters gathered, while crowds chanted, "Liar, liar, Maliki!" in the southern cities of Nasiriyah, Karbala and Kut.

In a bid to head off protests, Iraq slashed politicians' pay, increased food funds for the needy and delayed a planned law that would raise import tariffs and, thus, prices of goods in markets.