Around 460 people have been killed and 25,000 have been wounded -- most of them protesters -- since anti-government rallies erupted on October 1 in Baghdad and the Shiite-majority south.

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

"We strongly denounce the killings, abductions and attacks of all kinds that have been taking place," Sistani said in a sermon delivered by his representative in the shrine city of Kerbala during the weekly Friday prayer.

Protesters accuse pro-Iran armed factions of playing a role in the killing and abduction of protesters.

Sistani mentioned specifically an attack late last Friday when unidentified gunmen stormed and torched a multi-storey building known as Al-Sinek Garage in Baghdad where protesters had camped out for weeks.

At least 20 protesters and four police officers were killed and about 80 demonstrators abducted, medical sources and witnesses said.

The revered Shiite cleric also denounced Thursday's lynching by demonstrators of a teenager accused of attacking protesters in Baghdad, calling it "an atrocious crime".

Such actions "reaffirm once again the importance of what the marjaiyah (Shiite religious leadership) has repeatedly called for and that is that all weapons must be placed under the control of the state", he said.

Sistani urged authorities to assume their responsibilities and prosecute those responsible for the violence, and called on protesters to keep their demonstrations peaceful.

The mostly young protesters are angry at a government they see as corrupt and inefficient.

They have complained of unemployment in the oil-rich country and poor infrastructure including chronic power and water cuts.

Despite Iraq being a major oil producer, one in five of its people live in poverty and youth unemployment stands at 25 percent, the World Bank says.

Demonstrators have also turned their wrath against Iran, which wields tremendous sway among Iraqi politicians and military figures, particularly the Hashed al-Shaabi paramilitary forces.

At dawn on Friday, sound bombs exploded near pro-Iranian targets in the southern city of Amara without causing any casualties, security sources said.

Two of them targeted the homes of leaders of the Assaib Ahl al-Haq, one of the most powerful groups within the Hashed, and a third went off near the house of a member of Ansar Allah, another component of the group.

Protests meanwhile were reported in several cities in southern Iraq as well as in Baghdad's Tahrir Square.

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