Despite tear gas, water cannon and baking temperatures that touched 47 degrees Celsius (116 degrees Fahrenheit), they stormed the complex on Saturday after pulling down heavy concrete barricades on roads leading to Baghdad's fortified Green Zone of diplomatic and government buildings.

Nearly ten months after October elections, Iraq is still without a new government despite intense negotiations between factions.

Analysts have said Sadr, a mercurial cleric who once led a militia against US and Iraqi government forces, is using street protests to signal that his views must be taken into account in government formation.

The immediate trigger for the occupation was the decision by a rival Shiite bloc, which is pro-Iran, to pick Mohammed Shia al-Sudani for the prime minister's post.

On Sunday morning, the demonstrators marked the Muslim month of Muharram, a traditional Shiite celebration, with religious chants and collective meals.

"We were hoping for the best but we got the worst. The politicians currently in parliament have brought us nothing," said one of the protesters, Abdelwahab al-Jaafari, 45, a day labourer with nine children.

Volunteers distributed soup, hard-boiled eggs, bread and water to the protesters.

Some had spent the night inside the air conditioned building -- which dates from dictator Saddam Hussein's era -- with blankets spread out on the marble floors.

Others took to the gardens, on plastic mats under palm trees.

In multi-confessional and multi-ethnic Iraq, government formation has involved complex negotiations since a 2003 US-led invasion toppled Hussein.

Sadr's bloc emerged from elections in October as the biggest parliamentary faction, but was still far short of a majority.

In June his 73 lawmakers quit in a bid to break a logjam over the establishment of a new government.

That led to a pro-Iran block becoming the largest in parliament, but still there was no agreement on naming a new prime minister, president or cabinet.

The occupation that began on Saturday was the second time in days that Sadr's supporters had forced their way into the legislative chamber.

The protests are the latest challenge for a country trying to overcome decades of war and now facing the impact of climate change.

Despite oil wealth and elevated global crude prices, Iraq remains hobbled by corruption, unemployment and other problems, which sparked a youth-led protest movement in 2019.