Al Jazeera has obtained pictures which appear to show police shooting at protesters in the Iraqi city of Falluja, during Friday's deadly nationwide "day of rage".

An unprecedented lockdown of Iraq's capital failed to deter thousands of Iraqis from protesting, serving notice that the anti-government rage sweeping the Middle East will not be easily extinguished in Baghdad.

The "day of rage" protests rocked other Iraqi cities as well, as demonstrators burned or tried to storm government buildings from the southern port of Basra to the northern cities of Mosul and Falluja, where at least 12 protesters were shot dead by security forces.

Thousands rallied in cities across the country on Friday during what has been billed as the 'day of rage' [AFP]

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 a 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.

The next day, Iraq's Baiji oil refinery was shut down after fighters carried out a bomb attack and set it on fire, the governor of Salahuddin province said.

The refinery is situated in the town of Baiji, about 180km north of Baghdad.