Hundreds of supporters of Shiite Muslim cleric Moqtada al Sadr stormed Baghdad's Green Zone on Saturday and entered the parliament building after lawmakers failed to convene for a vote on overhauling the government.
The protesters, who had gathered outside the heavily fortified district housing government buildings and many foreign embassies, crossed a bridge over the Tigris River chanting, "The cowards ran away!" in apparent reference to lawmakers leaving parliament.
Around sunset security forces fired teargas and bullets into the air in an effort to stop more protesters from entering. Around a dozen people were wounded, police sources said.
Rioters rampaged through several parts of the building, damaging public property and causing a destruction.
A protest held outside the Green Zone escalated after parliament again failed to reach a quorum and approve new ministers to replace the current government of party-affiliated ministers.
All entrances of Baghdad were temporarily shut "as a precautionary measure to maintain the capital's security," a security official said
The unrest kicked off minutes after cleric Moqtada al Sadr wrapped a news conference in the holy Shiite city of Najaf during which he condemned the political deadlock, but did not order supporters to enter the Green Zone.
As night fell, demonstrators set up tents at a nearby parade ground under triumphal arches made from crossed swords held by hands modelled on those of Saddam Hussein, who was toppled by a controversial US invasion in 2003.
Supporters of Sadr have been demonstrating for weeks at the gates of the Green Zone, responding to their leader's call to pressure the government to reform.
Following the breach, Prime Minister Haider al Abadi inspected security forces inside the Green Zone, discrediting earlier reports that he had fled. He called on protesters to return to areas set aside for demonstrations and not to infringe on public property.
Videos showed protesters on Saturday beating a man in a grey suit and attacking an armoured SUV.
The source in Sadr's office said a Sadrist MP had escorted out several deputies, the last ones holed up in parliament, in his motorcade.
Some protesters stood atop concrete blast walls that form the district's outer barrier.
President Fuad Massoum called on demonstrators to leave parliament, but urged politicians to implement the cabinet reform: "Burying the regime of party and sectarian quotas cannot be delayed."
The Iraqi government has been in deadlock for months as parties failed to reach a deal to reform the government, which is structured according to a strict administrative power sharing agreement.
Inside parliament hundreds of protesters danced, waved Iraqi flags and chanted pro-Sadr slogans as some continued breaking furniture.
Local television showed them chanting and taking pictures of themselves inside the main chamber where moments earlier lawmakers had met.
Parliament failed to reach quorum on Saturday afternoon to complete voting on a cabinet reshuffle first urged by Abadi in February. A handful of ministers were approved on Tuesday despite disruptions by dissenting lawmakers.
Political parties have resisted Abadi's efforts to replace some ministers - chosen to balance Iraq's divisions along party, ethnic and sectarian lines - with technocrats in a bid to combat corruption.
Supporters of Sadr have been demonstrating in the capital for weeks, responding to their leader's call to put pressure on Prime Minister Abadi to follow through on months-old reform promises.