Hundreds of protesters were camping near parliament in the heavily fortified Green Zone in Baghdad on Sunday, a day after they stormed the assembly demanding reforms.
The protesters loyal to influential Shiite cleric Moqtada al-Sadr eventually left parliament on Saturday night, only to start an open-ended sit-in in a nearby square to push for long-delayed reforms.
Prime Minister Haider al-Abadi ordered authorities to arrest protesters who attacked security forces and lawmakers, and destroyed property during the breach.
"They must be referred to court to get fair punishment," al-Abadi said in a statement released by his office.
The premier inspected the parliament building once the demonstrators had left and checked the damage caused to some offices, state media reported.
On Saturday, thousands of al-Sadr's loyalists breached the Green Zone and descended on parliament, protesting the delay in approving a cabinet of independents proposed by al-Abadi.
The breach marked a dramatic escalation in the political crisis in Iraq, which is struggling against Islamist insurgents.
President Fouad Massoum has called al-Abadi and parliamentary Speaker Salim al-Jabouri for a crisis meeting on Sunday, a statement from the president's office said.
There is an increased deployment of security forces in the Green Zone, which houses government offices and foreign embassies.
No incidents have been reported between security personnel and those camping outside parliament.
For several months, Iraq has witnessed numerous demonstrations against corruption and inefficient public services.
In response, the Shiite prime minister proposed a package of major reforms, including the formation of a government of independent technocrats. But political blocs in parliament have thwarted the move.
Al-Abadi has warned that the current crisis can hamper the country's US-backed fight against the Islamic State extremist group, which controls key areas in Iraq's Sunni heartland.
Meanwhile, at least 11 people were killed Sunday in twin bombings in a mostly Shiite town in southern Iraq, a security official said.
The blasts were caused by a car bomb and an explosive device in the town of Samawa, some 300 kilometres south of the capital Baghdad, head of the local security committee Ahmed Manfi added.
At least 13 people were injured.
No one has claimed responsibility for the attack, which comes a day after 24 people were killed in a car bombing targeting Shiite pilgrims in a Baghdad suburban area.
That bombing was claimed by the Islamic State radical Sunni militia that regards Shiites as heretics.
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