Jeanine Hennis-Plasschaert, head of the UN Assistance Mission for Iraq, said on Saturday: "Five days of deaths and injuries: this must stop.
"Those responsible for the loss of life should be brought to justice," the BBC reported.
The protests against unemployment, poor public services and corruption in the country began in Baghdad on Tuesday before spreading to the other parts of the country.
It is the deadliest unrest since the Islamic State (IS) terror group was declared defeated in Iraq in 2017.
It is seen as the first major challenge to Prime Minister Adel Abdel Mahdi's fragile government, nearly a year since he came to power.
Authorities have been trying to control the protests through curfews and a near-total internet blackout.
The daytime curfew in Baghdad was lifted on Saturday, and smaller groups of protesters began to renew their action.
The city's Tahrir Square has been the focal point of protests, but it was blocked on Saturday, according to Iraqi media.
On Friday, Prime Minister Mahdi vowed to respond to protesters' concerns but warned there was no "magic solution" to Iraq's problems, the BBC reported.
He said he had given his full backing to security forces, insisting they were abiding by "international standards" in dealing with protesters.
Iraq has the world's fourth-largest reserves of oil, but 22.5 per cent of its population of 40 million were living on less than $1.90 a day in 2014, according to the World Bank.
One in six households has experienced some form of food insecurity.
The unemployment rate was 7.9 per cent last year, but among young people it was double that.
Almost 17 per cent of the economically active population is underemployed.
( With inputs from IANS )