Medical officials said at least 52 others were injured in the unrest on February 5.

The fighting marked the deadliest clash yet in the escalating tensions between Sadr, a radical cleric-turned-politician, and the largely leaderless rallies that have demanded the resignation of what they term government "elites."

The populist Sadr initially backed the demonstrations but split with them over the past few days, endorsing Muhammad Tawfiq Allawi, who has been designated the country's prime minister.

Iraqi President Barham Salih on February 1 appointed Allawi in hopes of ending more than two months of political deadlock.

Allawi will run the country until early elections are held. He has a month to form a new government.

In November, Adil Abdul-Mahdi resigned as prime minister amid the protests over corruption, falling living standards, and foreign influence in the country, particularly by Iran but also the United States. Nearly 500 protesters have been killed in a deadly crackdown by security forces.

In the latest clash between the rival groups, security sources told AFP that supporters of Sadr -- known as "Blue Hats" for the caps they often wear -- had attempted to clear the area of anti-government protesters when fighting broke out.

Sadr later appeared to attempt to calm his supporters, saying, "The 'Blue Hats' have a duty to peacefully secure schools and service centers, not to defend me or suppress the voices that chant against me."

Allawi condemned the violence and in a Twitter posting called on the country's caretaker cabinet to "protect protesters."

Sadr has said he opposes all foreign interference in Iraq, but he has aligned himself more closely with parties backed by Tehran in recent months.

He has backed Allawi's candidacy in an agreement with Iranian-backed parties that dominate Iraq's government and state institutions.

With reporting by Reuters, AP, AFP, and dpa