Hundreds of supporters of an influential Shia cleric camped inside Iraq’s parliament on Sunday, after toppling security walls around the building and storming the day before.

The protesters – supporters of Iraqi Shia cleric Muqtada al-Sadr – have pledged to stage an open-ended sit-in to derail efforts by their rivals from Iran-backed political groups to form the country’s next government.

The developments have catapulted Iraqi politics into the limelight, plunging the country deeper into political crisis as a power struggle unfolds between the two main Shia groups.

The sit-in on Sunday looked more like a joyful celebration than a political demonstration – supporters of Iraqi Shiite cleric Muqtada al-Sadr danced, prayed and chanted slogans inside parliament in praise of their leader.

In the meantime, they took a siesta on mattresses lining the large halls.

It was a starkly different scene from Saturday, when protesters used ropes and chains to tear down cement walls around Baghdad’s heavily fortified Green Zone, then stormed the assembly building. It was the second such breach last week, but this time they did not disperse peacefully.

Iraqi security forces fired tear gas and solar grenades initially in an attempt to repel protesters. The Health Ministry said around 125 people were injured in the violence – 100 protesters and 25 members of the security forces. Within hours, the police retreated, leaving parliament to the protesters.

Outside the building, rubbish from food parcels and other rubbish littered the street leading to the gates of parliament as trucks drove through giant cannons of steaming rice and beans to feed protesters.

There was also humor inside parliament on Sunday among al-Sadr supporters.

One protester, Haidar Jameel, took the seat of parliament speaker Mohammed Halbousi – among Iraq’s most powerful political figures – and from there watched his rambunctious comrades in the assembly.

After al-Sadr supporters took control of parliament, Halbousi suspended future sessions until further notice.

“This is an open sit-in, we won’t be back until our demands are met,” he said.

Cans of bottled water were piled up in the street and tents were erected. A small child was handing out candy, teenagers were selling bag juice.

The parliament takeover showed al-Sadr was using his broad supporters as a pressure tactic against his rivals in the coordination framework – an alliance of Iran-backed Shia parties led by former prime minister Nouri al -Maliki – after his party was unable to form a government despite winning the most seats in last October’s federal election.

Neither side appears willing to concede, and al-Sadr appears determined to derail efforts to form a government by Iran-backed groups.