The former Shiite militia leader, whose bloc is the biggest in parliament, said in a statement that in order to avoid further deaths "the government should resign and early elections should be held under UN supervision".

He said he could "not keep silent" as Iraqi blood was being shed.

At least 44 people, including six police, have been killed with hundreds wounded in four days, medical and security sources said.

Friday saw chaotic scenes of protests in Baghdad and other cities with at least 10 people killed, including four -- two police and two civilians -- who security forces said were shot dead by "unidentified snipers".

AFP journalists reported hearing rapid automatic rifle fire across the capital.

Sadr's statement piled new pressure on Prime Minister Adel Abdel Mahdi as he battles to quell the unrest.

It came after Shiite spiritual leader Grand Ayatollah Ali Sistani urged authorities in a midday sermon to heed the demands of demonstrators, warning the protests could escalate unless immediate and clear steps are taken.

In his first speech since protests began Tuesday, the embattled premier appealed for patience from the young unemployed who have formed the mainstay of the protests, saying his not yet year-old government needed more time to implement reforms.

But despite his plea, a curfew and an internet blackout, Iraqis thronged the iconic Tahrir Square on Friday and clashed with the anti-riot police, AFP reporters said.

Security forces opened up with a barrage of gunfire and reporters said they saw several people hit by bullets, some in the head and the stomach.

- 'We're not infiltrators' -

"We're not infiltrators," protesters in the capital shouted, responding to accusations from Iraqi officials that "aggressors" were behind the protests.

Demonstrator Sayyed told AFP the protests would continue "until the government falls".

Protests first broke out in Baghdad on Tuesday and have since spread across the Shiite-dominated south.

They are unusual because of their apparent spontaneity and independence in a country where rallies are typically called by politicians or religious figures.

Medical sources say that most of those killed were hit by live rounds but do not specify who was shooting.

The Iraqi human rights commission said wounded protesters were being arrested from hospitals, slamming a heavy handed approach by security forces.

In the southern city of Diwaniyah, where two people were killed on Friday, AFP reporters said protesters had breached the main gate at the governor's compound and were headed towards the main building.

The back-to-back messages from Sistani and Sadr were a huge blow to Abdel Mahdi's government.

Sistani has repeatedly acted as final arbiter of the politics of Iraq's Shiite community, which dominates the government.

And populist Sadr's Saeroon bloc emerged as the biggest in the Iraqi parliament after May 2018 elections.

His supporters have been at the forefront of most of the larger protests in recent years, including in 2016 when he urged them to storm Baghdad's administrative and diplomatic Green Zone.

Adel Mahdi on Friday asked for more time to implement his reform agenda in a country plagued by corruption and unemployment after decades of conflict.

"There are no magic solutions."

- 'Lethal force' -

In a live television address, parliament speaker Mohammad al-Halboussi assured protesters "your voice is being heard", adding that he was holding meetings with officials to discuss their grievances.

Riot police have unleashed water cannons, tear gas, rubber bullets and live fire to clear the streets of protesters.

As protests and clashes gained in intensity, many Baghdad shops and petrol stations remained shuttered Friday.

In a residential area near the protest site, crowds gathered to buy vegetables and fruit, with one shopkeeper saying the price of tomatoes, grapes and other greens had risen threefold.

Northern and western provinces that were ravaged in the 2014-2017 war against the Islamist State group have remained relatively quiet.

The United Nations and Amnesty International urged Iraqi authorities to respect the right of peaceful assembly.

"We are worried by reports that security forces have used live ammunition and rubber bullets in some areas, and have also fired tear gas canisters directly at protesters," Marta Hurtado, spokeswoman for the UN human rights office, told reporters in Geneva.

Amnesty International's Middle East research director Lynn Maalouf condemned the use of "lethal and unnecessary force".

An internet blackout was a "draconian measure... to silence protests away from cameras and the world's eyes", she added.