United Nations officials in Geneva said Friday that the Iraqi government was not doing enough to defuse the protests and had failed to rein in security forces and militias, some of which have fired live ammunition at protesters.
Protesters still occupy part of Al Jumhuriyah (Republic) Bridge, the southernmost of the capital's bridges and the closest to the main protest camp in Tahrir (Liberation) Square.
More than 140 people were wounded with many hit by gas canisters and shrapnel.
The government promised reforms aimed at ending the crisis.
An open fire in a street in Baghdad, Iraq, where the street is covered in shrapnel.
The Prime Minster said authorities would ban possession of weapons by non-state armed groups who have been accused of killing protesters, and that there would be investigations into demonstrator deaths.
Protesters, some of whom view Sistani as part of the political and religious system they say is the cause of many Iraqis' misery, took little solace from the cleric's words.
He added protests were a legitimate engine of political change but urged demonstrators not to interrupt "normal life".
The protests began in Baghdad and quickly spread to the country's southern provinces.
The capital and much of the country's Shia south have been rocked by a wave of demonstrations since 25 October, as anger mounts over deep-seated corruption, lack of public services and cronyism that has afflicted Iraq since the 2003 US-led invasion.
The current cycle of anti-government protests and the heavy-handed security crackdown has left more than 250 people dead.
In Basra, four people were killed on Thursday and two on Friday as security forces dispersed protesters.
"Police have re-taken nearly the entire area up ahead of us".
Many of them have cast the protests as a "conspiracy" to plunge Iraq back into the chaos that has gripped it for decades.
The demonstrators had thrown molotov cocktails and lit fires on the concrete blast walls around the offices, before security forces used tear gas and live rounds to disperse them.
At a nearby makeshift clinic, volunteer medic Manar Hamad said she had helped treat dozens of wounded on Saturday alone.
The sound of tear gas canisters and stun grenades reverberated around central Baghdad nightly over the past week.
Iraq's top Shiite cleric Ali al-Sistani said on Friday that Iraqi government has a unique opportunity to respond to demonstrators' demands, while warning of internal and external parties to exploit the demonstrations to achieve their goals.
Umm Qasr receives imports of grain, vegetable oils and sugar shipments that feed a country largely dependent on imported food.
A total of 23 protesters and security forces members have been killed and more than 1,077 injured amid ongoing demonstrations in Baghdad and southern provinces of Iraq from November 3 to 7, the Iraqi High Commission for Human Rights said Friday, Trendreports citingXinhua.