Fighting between rival Iraqi forces raged for a second day Tuesday with rocket fire echoing from Baghdad's Green Zone where 23 supporters of powerful Shia leader Moqtada Sadr have been shot dead, medics said.
Tensions have soared in Iraq amid a political crisis that has left the country without a new government, prime minister or president for months, and escalated sharply after Sadr's supporters on Monday stormed the government palace following their leader's announcement that he was quitting politics.
The violence pitches backers of Sadr against rival Shia factions backed by neighbouring Iran.
Overnight, shelling targeted the high-security Green Zone that houses government buildings and diplomatic missions, a security source said, amid angry protests after Sadr's surprise announcement.
At least seven shells fell in the high-security Green Zone, the security source said on condition of anonymity, but it was not immediately clear who was responsible.
The security source said Sadr's supporters opened fire at the Green Zone from the outside, adding security forces inside "were not responding."
After a lull in violence, fresh clashes between Sadr's supporters and the army and men of the Hashed al-Shaabi, former Tehran-backed paramilitaries integrated into the Iraqi forces, erupted again on Tuesday.
The rattle of automatic gunfire and heavier explosions of rocket-propelled grenades could be heard from the Green Zone, AFP correspondents reported.
The United Nations 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."
But amid an army-imposed nationwide curfew that continued on Tuesday, Baghdad was otherwise quiet, with shops shuttered and few cars venturing out on the streets.
On Tuesday, medics updated the toll of Sadr supporters killed to 23, with some 380 others injured -- some with bullet wounds and others suffering tear gas inhalation.
Witnesses said earlier that Sadr loyalists and supporters of a rival Shia 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.
The United States also urged calm amid the "disturbing" reports, while France called on "the parties to exercise the utmost restraint."