Jeanine Hennis-Plasschaert, who heads the UN's Iraq mission (UNAMI), said the country's authorities must "step up to the plate and make things happen".

"They are elected by the people, they are accountable to them," she said.

The UN has put forward a phased roadmap, backed by the country's top Shiite cleric Grand Ayatollah Ali Sistani, calling for an immediate end to violence, electoral reform and anti-graft measures within two weeks.

That would be followed by constitutional amendments and infrastructure legislation within three months.

Hennis-Plasschaert discussed the plan with lawmakers on the sidelines of a parliamentary session on Wednesday, telling them: "now is the time to act, otherwise any momentum will be lost -- lost at a time when many, many Iraqis demand concrete results."

Protests broke out in Baghdad and the country's Shiite-majority south in early October over rampant corruption, lack of jobs and notoriously poor services.

Protesters have escalated their demands to deep-rooted regime change, but political forces have rallied in recent days to prop up the government of Prime Minister Adel Abdel Mahdi.

Politicians closed ranks following a series of meetings with top Iranian general Qasem Soleimani, an extremely influential figure who often brokers deals among Iraq's fractured political class.

Hennis-Plasschaert told AFP on Wednesday she did not seek to be a counter-weight to Iranian influence but said she feared "spoilers" could prevent progress.

"This country unfortunately knows many actors, external, internal, that could act as spoilers (and) undermine the legitimate demands of the people," she said.