An influential Shiite cleric announced he would resign from Iraqi politics and hundreds of his angry followers stormed the government palace in response, sparking violent clashes with security forces in which at least 15 protesters were killed.

Medical officials said several protesters were wounded by gunfire and a dozen more were injured by tear gas and physical altercations with riot police in the protests that followed the announcement by Shiite cleric Muqtada al-Sadr.

Iraq’s military announced a nationwide curfew and the caretaker premier suspended cabinet sessions in response to the unrest.

Iraq’s government has been deadlocked since Mr 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.

To further his political interests Mr 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 groups, which they see as responsible for the status quo.

During Monday’s violence, hundreds of protesters pulled down the cement barriers outside the government palace with ropes and breached the palace 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.

An Associated Press photographer heard gunshots being fired and saw several wounded protesters bleeding and being carried away.

Protests also broke out in the Shiite-majority southern provinces, with Mr al-Sadr’s supporters burning tyres 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 against its influence in Iraq and has repeatedly attempted to broker dialogue with Mr al-Sadr.

In July, Mr al-Sadr’s supporters broke into the parliament to deter his rivals in the Co-ordination Framework, an alliance of mostly Iran-aligned Shiite parties, from forming a government.

Hundreds have been staging a sit-in outside the building for more than four weeks.

His bloc has also resigned from parliament.

The Framework is led by Mr al-Sadr’s chief nemesis, former prime minister Nouri al-Maliki.

This is not the first time Mr al-Sadr, who has called for early elections and the dissolution of parliament, has announced his retirement from politics – and many dismissed the latest 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 is a risky gambit and are worried how it will impact Iraq’s fragile political climate.

By stepping out of the political process, Mr al-Sadr is giving his followers, most disenfranchised from the political system, the green light to act as they see fit.

Mr 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.

Iraq’s military swiftly announced a nationwide curfew beginning at 7pm local time.

It called on the cleric’s supporters to withdraw immediately from the heavily fortified government zone and to practise 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 called on Mr al-Sadr to request his followers to withdraw from government institutions.

He also announced cabinet meetings would be suspended.

The cleric announced his withdrawal from politics in a tweet, and ordered the closure of his party offices.

Religious and cultural institutions will remain open.

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.

Mr al-Sadr’s announcement on Monday appeared to be in part a reaction to the retirement of Shiite spiritual leader Ayatollah Kadhim al-Haeri, who counts many of Mr al-Sadr’s supporters as followers.

The previous day, Ayatollah al-Haeri announced 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 centre in Iraq’s holy city of Najaf.

The move was a blow to Mr al-Sadr.

In his statement he said Ayatollah al-Haeri’s stepping down “was not out of his own volition”.