The Iraqi army has declared a curfew in Baghdad after security forces opened fire to stop protesters storming the Green Zone, reportedly injuring dozens.
They fired tear gas and live bullets to drive back the mainly Shia Muslim crowds, as they protested against corruption and security failures.
Shia Muslim cleric Moqtada Sadr condemned the use of force.
It was the second time this month that protesters had managed to break into the city’s government area.
Mr Sadr voiced support for the demonstrators’ “peaceful [and] spontaneous revolt”.
At least 50 demonstrators are said to have been wounded.
The protesters accuse the government of neglecting much-needed reforms, as it struggles with its campaign against the so-called Islamic State group (IS) and declining oil revenues.
The Sunni jihadist group controls parts of western and northern Iraq and has been behind a wave of recent attacks that have left dozens killed.
Some demonstrators managed to break into the prime minister’s office and parliament.
Baghdad’s Green Zone houses the parliament, key government buildings and many foreign embassies.
The authorities later said they had completely regained control of the area and the protesters had withdrawn.
The curfew on the capital will remain in place until further notice, state TV reported.
Security personnel have been asking shops to close down and have been blocking streets with concrete blast walls, residents told AFP news agency.
Who is Moqtada Sadr?
The Shia cleric and his militia group, the Mehdi Army, gained prominence after the US-led invasion of Iraq in 2003. galvanising anti-US sentiment.
Mr Sadr’s followers clashed repeatedly with US forces, whose withdrawal the cleric consistently demanded.
An arrest warrant was issued for Mr Sadr in 2004 in connection with the murder of a rival cleric.
His militia was also blamed for the torture and killing of thousands of Sunnis in the sectarian carnage of 2006 and 2007. Mr Sadr fled to Iran during that period.
In 2011, Mr Sadr returned from his self-imposed exile to Iraq, taking a more conciliatory tone and calling for Iraqi unity and peace.
Prime Minister Haider al-Abadi, who came to power in 2014, has promised to stamp out corruption and ease sectarian tensions.
He has been pressing for radical reforms and wants to form a government of technocrats, but has been blocked by lawmakers, the BBC’s Jim Muir in Baghdad reports.
Parliament is so deeply split that it cannot hold a meeting because no side can gather a quorum, our correspondent adds.
Iraq’s system of sharing government jobs has long been criticised for promoting unqualified candidates and encouraging corruption.
The government is carefully balanced between party and religious loyalties but the country ranks 161st of 168 on corruption watchdog Transparency International’s corruption perceptions index.