Mohammed al-Doujaili, 24, was shot in the back near the Tahrir Square protest hub on Saturday night, the police source said.

Another man who was with him was wounded in the same attack, and al-Doujaili died of his wounds at a Baghdad hospital Sunday morning, relatives said.

Doujaili, who helped distribute food to protesters encamped in Tahrir Square, was buried in Baghdad's Shiite-dominated district of Sadr City.

He is the fourth protester to be killed by unidentified assailants over the past two weeks.

Father of five Ali al-Lami was shot and killed by several bullets to the head earlier this week and prominent civil society activist Fahem al-Tai was killed in a drive-by shooting in Iraq's shrine city of Karbala.

In one particularly gruesome case, the bruised body of 19-year-old Zahra Ali was found on December 2 outside her family home in Baghdad, hours after she had gone missing.

Iraq's capital and its Shiite-majority south have been gripped by more than two months of rallies against corruption, poor public services and a lack of jobs.

Around 460 people have been killed and 25,000 wounded, most of them protesters, since the youth-led rallies erupted on October 1.

Since then demonstrators in the capital and southern cities have disappeared almost daily, in most cases taken from near their homes as they returned from protests.

Protesters accuse pro-Iran armed factions of playing a role in the killings and abductions.

London-based rights group Amnesty International on Friday urged Baghdad to clamp down on what it called a "campaign of terror targeting protesters".

Demonstrations once again took place on Sunday in Baghdad and across the south of Iraq, where schools and public administrations remained closed, AFP correspondents said.