Thirty supporters of Shiite leader Moqtada Sadr have been shot dead in nearly 24 hours of fighting between rival Iraqi forces that has since died down, according to the latest toll from medics.
At least 570 others were injured in the violence that erupted in Baghdad's Green Zone, pitting Sadr loyalists against Shiite factions backed by neighbouring Iran.
Fighting ended today after Sadr ordered his supporters to withdraw.
Moments after his speech was broadcast live on television, his supporters were seen beginning to leave the Green Zone, and minutes after that, the army lifted a nation-wide curfew.
Mr Sadr, a grey-bearded preacher with millions of devoted followers who once led a militia against American and Iraqi government forces after the 2003 US-led overthrow of dictator Saddam Hussein, gave followers "60 minutes" to withdraw after which he would threaten to "disavow" those who remained.
"I apologise to the Iraqi people, the only ones affected by the events," Mr Sadr said in a speech from his base in the central city of Najaf.
"Shame on this revolution... Regardless of who was the initiator, this revolution, as long as it is marred by violence, is not a revolution," he said.
"I thank the security forces and members of Hashed al-Shaabi," he added.
Tensions have soared in Iraq amid a political crisis that has left the country without a new government, prime minister or president for months.
They escalated sharply after Sadr's supporters on Monday afternoon stormed the government palace inside the high-security Green Zone following their leader's announcement that he was quitting politics.
'Dangerous escalation'
Overnight, shelling targeted the Green Zone that houses government buildings and diplomatic missions, amid angry protests after Sadr surprised many by announcing his "definitive retirement".
Violence continued this morning - with the rattle of automatic gunfire and heavier explosions of rocket-propelled grenades - as Sadr's supporters clashed with the army and men of the Hashed al-Shaabi, former Tehran-backed paramilitaries integrated into the Iraqi security forces.
The UN mission in Iraq warned of "an extremely dangerous escalation" and called on all sides to "refrain from acts that could lead to an unstoppable chain of events".
"The very survival of the state is at stake," it warned.
This morning, medics said 23 Sadr supporters had been killed and some 380 others wounded - some with bullet wounds and others suffering tear gas inhalation.
A mass funeral was held today in the Shiite holy city of Najaf for some of the protesters killed in Baghdad.
Witnesses said earlier that Sadr loyalists and supporters of a rival Shiite bloc, the pro-Iran Coordination Framework, had exchanged fire.
The Framework condemned an "attack on state institutions", urging the Sadrists to engage in dialogue.
Caretaker Prime Minister Mustafa al-Kadhemi said "security or military forces, or armed men" were prohibited from opening fire on protesters.
'Disturbing'
The United States also urged calm amid the "disturbing" reports, while France called on "the parties to exercise the utmost restraint".
Shortly after Sadr announced he was stepping down, his followers burst into the Republican Palace in Baghdad - where cabinet meetings are usually held.
Mr Sadr - a longtime player in the war-torn country's political scene, though he himself has never directly been in government - announced he was quitting politics two days after he said "all parties" including his own should give up government positions in order to help resolve the political crisis.
His bloc emerged from last October's election as the biggest in the legislature, with 73 seats, but short of a majority.
Since then the country has been mired in political deadlock due to disagreement between Shiite factions over forming a coalition.
In June, his lawmakers quit in a bid to break the logjam, which led to the Coordination Framework becoming the largest bloc.
Sadr's supporters have for weeks been staging a sit-in outside Iraq's parliament, after storming the legislature's interior on 30 July, demanding fresh elections be held.
The Coordination Framework wants a new head of government to be appointed before any new polls are held.
