Iraq was rocked by protests during the first week of October, with thousands taking to the streets of Baghdad and the country's south to demand jobs, services and an end to corruption.

The protests quickly turned bloody, with an official toll citing 157 people killed, mainly protestors in the capital.

The government held an enquiry into the violence, producing a report on Tuesday that condemned "excessive use" of force by security personnel but also cited unknown "shooters" that authorities have neither identified nor arrested.

Haider al-Abadi, prime minister from 2014 to 2018 and now in opposition, slammed the government on Twitter, saying it should "resign and apologise to the people".

"The government investigation does not reveal who was actually responsible for giving the order to kill protestors," he added.

Abadi said that the fact that protestors were targeted in several provinces indicated there had been "orders from a high central authority".

Former prime minister Nuri al-Maliki's State of Law Alliance criticised the report as "obscure", saying it "does not respond to everyone's concerns and in particular, those of Grand Ayatollah Ali Sistani", the spiritual leader of Iraq's Shiite majority.

Sistani -- who wields significant political power -- had given the government a Friday deadline to respond to protestor demands and to shed light on the violence.

With further protests expected following the weekly Islamic prayers, Sistani is expected to give a Friday sermon that could serve to mobilise or deter demonstrators.

Independent lawmaker Maytham al-Joubouri said "the results of the investigation have little importance for the protestors".

"Blood was spilt and it will be difficult for the families to accept" such a report if "the criminals that killed protestors" are not clearly identified, he told AFP.

Shiite leader Ammar al-Hakim, also in opposition, stopped short of calling for further protests, but said on Twitter, "we will not stop our supporters from protesting in a personal capacity".

Influential Shiite cleric Moqtada al-Sadr already gave his numerous followers the green light to take to the streets again, having also called for the resignation of the government, to which his bloc belongs.

On Tuesday, Sadr upped the pressure by telling his supporters, militia units and lawmakers to be on "alert from Thursday evening until further notice".

On Saturday, parliament, paralysed by divisions since the start of October, said it would meet to discuss protestors' demands.