Meanwhile, Iraqi officials express "deep regret" at the death of protesters during weeks of unrest but defended Baghdad's handling of the situation.
The top UN official in Iraq and the country's most senior Muslim cleric on Monday urged authorities to get "serious" about reforms after anti-government demonstrations that have cost hundreds of lives.
Mass rallies calling for an overhaul of the ruling system have rocked the capital Baghdad and the country's Shiite-majority south since October 1 – the largest and deadliest popular movement in Iraq in decades.
The bloody unrest has sparked serious concern from the United Nations, human rights groups and the White House, which has called on Iraq "to halt the violence against protesters" and to pass electoral reform.
Iraqi officials expressed "deep regret" at the death of protesters during weeks of unrest but defended Baghdad's handling of the situation.
After weeks of paralysis, top leaders seem to have agreed to keep the system intact, but the UN in Iraq (UNAMI) urged them to enact a host of changes.
These include electoral reforms within two weeks, the prosecution of those responsible for the recent bloodshed as well as of corrupt officials, and the passing of anti-graft laws.
On Monday, UNAMI chief Jeanine Hennis-Plasschaert met the country's highest Shia authority, Grand Ayatollah Ali Sistani, in the holy city of Najaf.
She said the seat of Shia religious power in Iraq, known as the marjaiyah, had stressed that "peaceful demonstrators cannot go home without sufficient reforms" to answer their demands.
"The marjaiyah expressed its concerns that the political forces are not serious enough to carry out such reforms," said Hennis-Plasschaert.
"If the three authorities -- executive, judiciary and legislative -- are not able or willing to conduct these reforms decisively, there must be a way to think of a different approach," she warned.
There was no statement attributable directly to Sistani, who is 89 and never appears in public.
In his recent sermons, delivered by a representative, Sistani has described the protesters' demands as "legitimate" and called for the rallies to be handled with "restraint".
Parliament will meet on Wednesday for a session on the current crisis, the speaker announced on Monday, adding that Hennis-Plasschaert would attend.
Rallies flare up
At least 18 protesters have been killed since Saturday as security forces have cracked down on demonstrators.
They have forcibly cleared streets and squares in Baghdad, in the port hub of Basra and the southern city of Nasiriyah, where four protesters were shot dead on Sunday.
Security forces there even chased demonstrators into a children's hospital and fired tear gas inside.
Protesters struggled to come out in large numbers Monday in Nasiriyah and security forces reopened roads in Basra, stifling attempts to stage sit-ins near the provincial headquarters.
In Baghdad, live rounds rang out in neighbourhoods close to the main protest camp of Tahrir (Liberation) Square.
But thousands of demonstrators took to the streets again in Hillah, Kut and Diwaniyah – where the local teachers union announced it would begin a general strike on Tuesday.
Aside from the crackdown, activists and volunteer medics have described a widening campaign of arrests and intimidation intended to keep them away from protests.
The UN has warned that "a climate of anger and fear has set in".
Officials express regret at protester deaths
Iraq's Justice Minister Farooq Ameen Othman on Monday expressed "deep regret" over the loss of life during a meeting at UN headquarters in Geneva.
More than 300 people have been killed since the protests erupted on October 1.
At a UN review of member states' huma n rights records in Geneva, diplomats from several countries accused the Iraqi government of using excessive force.
Justice Minister Othman acknowledged there had been "individual violations" by members of the law enforcement agencies but said they were being investigated.
"...We would like to express our deep regret for the number of people killed," he told international diplomats gathered at what the UN calls the Universal Periodic Review.
"Our constitution guarantees peaceful assembly and the objective of our authorities is to protect the protesters, " he said.
Other Iraqi officials said plans were under way to free detained protesters and for electoral reform, both of which were among a package of reforms urged by the United Nations.
'We want total change'
Iraq's President Barham Saleh last month proposed an early vote after reforms, but the idea seems to have been widely rejected by the political class.
Prime Minister Adel Abdel Mahdi cast the proposal as unrealistic and even firebrand cleric Moqtada Sadr, who first demanded snap elections supervised by the UN, has gone silent.
The initial fissures among the political elite appear to have closed this week following a consensus brokered by Major General Qassem Soleimani, the head of Iran's Islamic Revolutionary Guard Corps' foreign operations arm.
Soleimani, who often appears in Baghdad at times of political crisis, has reportedly led a series of meetings with Iraq's top-tier politicians.
The agreement, they said, included a series of reforms in exchange for keeping the broader system in place.
Those proposals will likely fall short of the demands of protesters, who demand a complete overhaul of a regime they see as deeply corrupt.
Demonstrators say the current system means government jobs are doled out based on bribes or nepotism, shutting out applicants who are politically independent.
Youth make up 60 percent of Iraq's nearly 40 million people and the unemployment rate among them stands at a staggering 25 percent, according to the World Bank.
One in five people lives below the poverty line, despite the vast oil wealth of OPEC's second biggest producer.