The renewed violence has set Iraq on edge, with many fearing another destabilized phase after two decades of almost constant fighting.
Clashes between pro-Iranian security forces and armed supporters of the influential Shiite cleric Muqtada al-Sadr raged in Baghdad for a second day on Tuesday and the death toll rose to 24 as Iraq descended into a new round of chaos set off by months of failed efforts to form a government.
The violence began on Monday after Mr. Sadr declared that he was quitting Iraqi politics for good and his followers poured into the streets of Baghdad to protest, storming government buildings. Iran-backed units within the security forces opened fire on them and later, armed members of Mr. Sadr’s militia joined in the melee, exchanging fire with the security forces.
On Monday, officials said at least 12 people had been killed. But the fighting continued overnight and on Tuesday, a Health Ministry official said at least 24 people had been killed and more than 190 injured since Mr. Sadr’s supporters entered the heavily fortified Green Zone, home to Iraqi government offices, the United Nations and diplomatic missions including the U.S. Embassy.
On Tuesday, Baghdad was under strict curfew for the second straight day to tamp down violence.
The clashes have set Iraq on edge, with some fearing the country could descend into another violent phase after two decades of almost constant fighting. Following the U.S. invasion of Iraq in 2003, a civil war broke out and then a yearslong battle to drive out Islamic State after the terrorist group took over large parts of the country.
Although political turmoil and street protests are common in Iraq, this fighting could mark an even more dangerous and unstable phase, fueled by political paralysis, divisions among Shiites and the breaching of state institutions.
Elections last year in October were seen as a fresh start for the country — a response to massive protests against a corrupt and dysfunctional government. Instead they have led to a political deadlock.
Mr. Sadr, whose bloc won the most seats in Parliament, had tried in vain for months to form a coalition government with other partners after the elections. Frustrated over the failure, he urged his followers into the streets instead to achieve their aims. Mr. Sadr comes from a revered Shiite family of clerics and commands millions of followers in Iraq.
The clashes over the past day mainly pitted Iran-backed paramilitary units that are part of Iraqi government security forces against armed members of Mr. Sadr’s paramilitary organization, the so-called Peace Brigades, attacking each other’s positions and offices, according to Sajad Jiyad, an Iraq-based fellow with the Century Foundation.
A senior Iraqi security official said some of those killed on Monday had been shot by pro-Iran militia members who are part of Iraqi security forces as they approached the home of the former prime minister Nuri Kamal al-Maliki. The official asked not to be identified because of the sensitivity of the issue.
Neighboring Iran, which has exerted extensive efforts over the past several years to bring Shiite factions in Iraq closer together, reacted with alarm to the fighting, closing its borders with Iraq and telling Iranians it would work to bring them home safely.
A spokesman for the U.S. National Security Council said Monday that the United States was monitoring clashes but there was no current indication that the embassy would need to be evacuated.
The United Nations mission in Iraq called the clashes a dangerous escalation.
Falih Hassan and Nermeen al-Mufti contributed reporting from Baghdad