BAGHDAD — At least 23 people have died and hundreds more are injured after Iraq's capital descended into chaos on Monday over the resignation of an influential Shiite cleric.

Hundreds of protestors loyal to cleric Muqtada al-Sadr, stormed the Iraq government palace in Baghdad's Green Zone, sparking clashes with security forces which have left scores dead and nearly 400 people wounded.

Iraq's military announced a nationwide curfew, and the caretaker premier suspended cabinet sessions in response to the violence.

Medical officials said at least 380 protesters were wounded by gunfire or injured by tear gas and physical altercations with riot police.

The episode began when supporters of al-Sadr, who announced he would retire from domestic politics, pulled down the cement barriers outside the government palace with ropes and breached its gates. Many rushed into the lavish salons and marbled halls of the palace, a key meeting place for Iraqi heads of state and foreign dignitaries.

This sparked a harsh response from security forces, who shot and beat protestors.

Late Monday evening, mortar shells and automatic weapon fire could be heard from within the ultra-secure Green Zone, which houses government ministries and embassies.

Iraq's government has been deadlocked since al-Sadr's party won the largest share of seats in October parliamentary elections but not enough to secure a majority government.

His refusal to negotiate with his Iran-backed Shiite rivals and subsequent exit from the talks has catapulted the country into political uncertainty and volatility amid intensifying intra-Shiite wrangling.

Al-Sadr, a nationalist and a reformist

Iraq's majority Muslim population is split into followers of two distinct religious teachings, Shiites and Sunnis.

Recently, the Shiites have faced significant infighting, with the dispute centering around power and state resources but also influence over the Shiite street.

To further his political interests, al-Sadr has wrapped his rhetoric with a nationalist and reform agenda that resonates powerfully among his broad grassroots base, who hail from Iraq's poorest sectors of society and have historically been shut out from the political system.

They are calling for the dissolution of parliament and early elections without the participation of Iran-backed Shiite groups, which they see as responsible for the status quo.

During Monday's clashes, Saraya Salam, a militia aligned with al-Sadr, gathered in the capital's Tahrir Square to "protect" protesters, one of its commanders said.

An AP photographer heard gunshots being fired in the capital and saw several protesters bleeding and being carried away. It was not immediately clear who fired the gunshots. A senior medical official confirmed at least five protesters were killed by gunfire.

Protests also broke out in the Shiite-majority southern provinces, with al-Sadr's supporters burning tires and blocking roads in the oil-rich province of Basra and hundreds demonstrating outside the governorate building in Missan.

Iran considers intra-Shiite disharmony as a threat to its influence in Iraq and has repeatedly attempted to broker dialogue with al-Sadr.

In July, Al-Sadr's supporters broke into the parliament to deter his rivals in the Coordination Framework, an alliance of mostly Iran-aligned Shiite parties, from forming a government.

Hundreds have been staging a sit-in outside the building for over four weeks. His bloc has also resigned from parliament. The Framework is led by al-Sadr's chief nemesis, former Prime Minister Nouri al-Maliki.

This is not the first time al-Sadr, who has called for early elections and the dissolution of parliament, has announced his retirement from politics — and many dismissed Monday's move as another bluff to gain greater leverage against his rivals amid a worsening stalemate. The cleric has used the tactic on previous occasions when political developments did not go his way.

But many are concerned that it's a risky gambit and are worried about how it will impact Iraq's fragile political climate. By stepping out of the political process, al-Sadr is giving his followers, the most disenfranchised from the political system, the green light to act as they see fit.

Al-Sadr derives his political power from a large grassroots following, but he also commands a militia. He also maintains a great degree of influence within Iraq's state institutions through the appointments of key civil servant positions. His Iran-backed rivals also have militia groups.

Following the announcement of the 7 p.m. curfew (6 pm CET), Iraq's military swiftly called on the cleric's supporters to withdraw immediately from the heavily fortified government zone and to practice self-restraint "to prevent clashes or the spilling of Iraqi blood," according to a statement.

"The security forces affirm their responsibility to protect government institutions, international missions, public and private properties," the statement said.

Iraq's caretaker Prime Minister Mustafa al-Kadhimi also demanded that al-Sadr called on his followers to withdraw from government institutions.

The UN mission in Iraq said Monday's protests were an "extremely dangerous escalation" and called on demonstrators to vacate all government buildings to allow the caretaker government to continue running the state.

It urged all to remain peaceful and "refrain from acts that could lead to an unstoppable chain of events." "The very survival of the state is at stake," the statement said.

Al-Sadr announced his withdrawal from politics in a tweet and ordered the closure of his party offices. Religious and cultural institutions will remain open, it said.

The true motivations behind al-Sadr's announcement appeared to be a reaction to the retirement of Shiite spiritual leader Ayatollah Kadhim al-Haeri, who counts many of al-Sadr's supporters as followers.

In a surprise announcement Sunday, al-Haeri said he would be stepping down as a religious authority for health reasons and called on his followers to throw their allegiance behind Iran's Ayatollah Ali Khamenei rather than the Shiite spiritual center in Iraq's holy city of Najaf.

The move was a blow to al-Sadr, who, despite harboring ambitions to be a religious authority, lacks the scholarly credentials to be an ayatollah.

Al-Haeri, who resides in the Iranian holy city of Qom, once provided him with the legitimacy he lacked by designating al-Sadr as his representative in Iraq. He cut ties shortly after with the cleric but continued to enjoy the support of his followers.

By calling on his followers to side with Khamenei, al-Haeri brought on a crisis of legitimacy for al-Sadr.

In his tweet, al-Sadr said al-Haeri's stepping down "was not out of his own volition". — Agencies