Demonstrators have breached Baghdad’s heavily fortified Green Zone to protest against the selection of a nominee for prime minister by Iran-backed parties.
Riot police used water cannon on people who were trying to pull down cement blast walls.
But many breached the gates to the area, which houses government buildings and foreign embassies.
In the biggest protest since federal elections were held in October, the protesters walked down the zone’s main thoroughfare, with dozens gathering outside the doors to the parliament building.
The demonstrators were protesting the recent nomination of Mohammed al-Sudani as the official nominee of the Coordination Framework bloc, a coalition led by Iran-backed Shiite parties and their allies.
They crowded around two entrances to the Green Zone, with some scaling the cement wall and chanting: “Sudani, out!”
Caretaker Prime Minister Mustafa al-Kadhimi called for calm and restraint, and for protesters to “immediately withdraw” from the area.
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The demonstrators were largely followers of influential Shi’ite cleric Muqtada al-Sadr, who recently stepped down from the political process despite having won the most seats in the October federal election.
In 2016, al-Sadr supporters stormed the parliament in a similar fashion.
They staged a sit-in and issued demands for political reform after then-prime minister Haidar al-Abadi sought to replace party-affiliated ministers with technocrats in an anti-corruption drive.
Mr al-Sudani was selected by State of Law leader and former premier Nouri al-Maliki.
Before Mr al-Sudani can face parliament to be seated officially as premier-designate, parties must select a president.
Mr al-Sadr exited government formation talks after he was not able to persuade enough legislators to choose him as Iraq’s next president.
By replacing his legislators, the Framework leader pushed ahead to form the next government.
Many fear doing so also opens the doors to street protests organised by Mr al-Sadr’s large grass roots following and instability.