"We call on the Iraqi Government to allow people to freely exercise their rights to freedom of expression and peaceful assembly," Marta Hurtado, spokeswoman for the UN rights office, told journalists in Geneva.

Her appeal came as protesters continued to clash with anti-riot police on a fourth day of mass rallies that have left 34 people dead, according to an AFP count.

Hurtado said the UN rights office had independently confirmed 12 of those deaths in Baghdad, adding that "hundreds of other people have reportedly been injured, including members of the security forces".

"Dozens of demonstrators have been detained, although most were subsequently released," she said.

Demonstrations over corruption, unemployment and lacking services first broke out in Baghdad on Tuesday and have since spread to the Shiite-dominated south, while the northern and western provinces have remained relatively quiet.

They are unprecedented because of their apparent spontaneity and independence in a country where rallies are typically called by politicians or religious figures.

"We are worried by reports that security forces have used live ammunition and rubber bullets in some areas, and have also fired tear gas cannisters directly at protestors," Hurtado said, insisting that in dealing with demonstrations, "the use of force should be exceptional".

"Any use of force must comply with applicable international human rights norms and standards," she said, stressing that firearms should never be used "except as a last resort to protect against an imminent threat of death or serious injury."

"All incidents in which the actions of security forces have resulted in death and injury should be promptly, independently and transparently investigated," she said.

The UN rights office stressed that the demonstrators' demands for economic and social rights to be respected were "legitimate".

"People's grievances need to be heard," Hurtado said.

The UN was also deeply concerned about the detention of at least three journalists, two of whom had subsequently been released, warning that this risked "deterring other journalists from reporting on the situation".

Cuts to internet service across much of the country was also of concern, Hurtado said, stressing that "blanket internet shutdowns are likely to contravene freedom of expression."