"Five days of reported deaths and injuries; this must stop," Jeanine Hennis-Plasschaert, the special representative of the UN secretary general in Iraq, said in a tweet.

According to the Iraqi parliament's human rights commission, 99 people have been killed and nearly 4,000 wounded since protests against unemployment and living conditions erupted Tuesday in Baghdad before spreading to the south of the country.

The UN official said she was "deeply saddened by the loss of life".

"I call on all parties to pause and reflect. Those responsible for violence should be held to account. Let the spirit of unity prevail across #Iraq," she said.

The protests over chronic unemployment and poor public services that began Tuesday have escalated into a broader movement demanding an end to official corruption and a change of government.

They have been largely spontaneous and led by mainly young male protesters who have insisted their movement is not linked to any party or religious establishment.

The protests have presented the biggest challenge yet to Iraqi Prime Minister Adel Abdel Mahdi, who came to power a year ago as a consensus candidate promising reforms.

On Friday the premier appealed for more time to implement his reform agenda in a country devastated by decades of conflict.

"There are no magic solutions", he said.

But his pleas for patience appear to have underestimated the intensity of public anger, and several top figures have thrown their support behind the protesters.

Firebrand cleric Moqtada Sadr -- whose bloc of 54 lawmakers is the largest in parliament -- called on the government to resign and for snap elections to be held under UN supervision.

Sadr's movement has the power and organisation to bring large numbers of supporters onto the streets.

Iraq's Shiite spiritual leader Grand Ayatollah Ali Sistani used his weekly Friday sermon to urge authorities to heed the demands of demonstrators, warning the protests could escalate unless clear steps are taken immediately.

And parliament speaker Mohammed al-Halbusi vowed to push for reforms over employment and social welfare, telling protesters "your voice is being heard".

But the protesters who have hit the streets over the last five days have been contemptuous of existing political factions in the country.