Iraqi authorities committed serious human rights violations and abuses in their response to a wave of anti-government protests earlier this month that saw 149 civilians killed, the United Nations said.

In a report by its Human Rights Office published late on Monday, the UN Assistance Mission for Iraq (UNAMI) said there was evidence security forces had used excessive force against protesters and made mass arrests. There were also reports that security forces had denied protesters medical treatment, it said.

"UNAMI's interim findings indicate that serious human rights violations and abuses have been committed in the context of the demonstrations in Iraq," the report concludes.

"The number of dead, the extent and scale of injuries inflicted on demonstrators, all suggest that Iraqi security forces have used excessive force against demonstrators in Baghdad and elsewhere in Iraq."

Protests about high unemployment, poor public services and corruption erupted on Oct. 1, prompting a violent security crackdown. Protesters blame graft and infighting among political leaders for failing to improve their lives even in peacetime, two years after ISIS was declared defeated in Iraq.

Mourners carry the Iraqi flag-draped coffin of a protester killed during anti-government clashes. The funeral was held in the central Iraqi city of Najaf on Oct. 4. (Haidar Hamdani/AFP via Getty Images)

UNAMI said it conducted 145 interviews with human rights monitors, journalists, civil society activists, protesters, family members of killed demonstrators and others.

Journalists who covered the protests told UNAMI they were subjected to arrests, threats, intimidation and harassment. Human rights activists said they received warnings and death threats not to participate in demonstrations.

An Iraqi government committee investigating the wave of unrest found 149 civilians were killed because security forces used excessive force and live fire to quell protests, according to its report.

Over 70 per cent of deaths were caused by shots to the head or chest, and there was evidence of sniper fire targeting protesters, the government report said.

"The loss of life, serious injuries and harm resulting from the violence during the demonstrations was both tragic and preventable," said Danielle Bell, UNAMI's human rights chief.

"Concrete steps to enable peaceful assemblies and protect those participating should be a priority."